Carotenoids

Carotenoids 

(A group of highly specialized tetraterpenoids)

Introduction

These are fat soluble or yellow pigments present in plants & animals including bacteria these may be present along with chlorophyll (carotene & lutein) or may be present without chlorophyll. The carotenoid acts as photo sensitizer in conjugation with chlorophyll. When chlorophyll is absent (Fungi), then the carotenoids are mainly responsible for color. Carotenoids are also known as Lipochromes or chromo lipids because they are fat soluble pigments. They give a deep blue color with conc. H₂SO₄ & with a chloroform solution of antimony trichloride this Carr-Price reaction is the basis of the one method of the quantitative estimation of carotenoids. Some carotenoids are hydrocarbons, these are known as carotenes. Other carotenoids are oxygenated derivatives of the carotenes these are xanthophylls. These are also xanthophyll esters which are the natural ester of hydroxy carotenoids.

                                 Examples carotenoid & xanthophyll pigments from plants

Finally, there are some natural polyenes which contain fewer than 40 carbon atoms but structurally related to carotenoids. These are generally classified as the apocarotenoids & contains aldehyde or carboxyl group e.g. bixin (Annatto), Crocetin. When the loss of carbon atoms occurs at one end of the C₄₀ chain, this is shown by a numeral which follows the prefix apo & indicates the last carbon atom remaining from the present carotenoids e.g. β-apo-12 carotenal.

Carotenoid in fungi

These are tetraterpenoids main structure shows highly branched carbon skeleton composed of isoprene units, the center of molecule is formed by linkage of two isoprene unit tail to tail while others are head to tail. Hence central portion of molecule has 1, 6   position of methyl groups. Structurally these are polyenes having long conjugated chain in center of molecule. This portion which has extended conjugation is responsible for color of carotenoids of at the two ends are present two open chain structure or one open chain & other ring or two ring structure. Hence the basic structure of carotenoids becomes

Carotenoids are also known as Lipochromes or chromo lipids because they are fat soluble pigments. Carotenoids comprise of an important & unique class of carotenoids (C-40 terpenoids) in which two methyl group nearest the center of molecule are in position 1:6 while all the  other side chain methyl group occupies 1:5 position. Due to present of 3 isoprene units in structure they may also be regarded as tetra terpenoid. 

Enzyme Immobilization

Enzyme Immobilization

Microbial enzymes are most extensively employed in the food and beverage industries across the globe to meet the ever increasing demand for nutritionally superb and high-value products. In actual practice, the soluble enzymes engaged in ‘batch operations’ is found to be not-so-economical due to the fact that the active enzyme is virtually lost (not recovered) after each viable reaction. Therefore to overcome this problem we are immobilized enzymes after reaction & reuse them.

Immobilized enzymes have been defined as enzymes that are physically confined or localized, with retention of their catalytic activity, and which can be used repeatedly and continuously and the process is called enzymes immobilization.

There is a variety of methods by which enzymes can be localized, ranging from covalent chemical bonding to physical entrapment however they can be broadly classified as follows:

1. Covalent bonding of the enzyme to a derivatized, water-insoluble matrix.

2. Intermolecular cross-linking of enzyme molecules using multi-functional reagents.

3. Adsorption of the enzyme onto a water-insoluble matrix.

4. Entrapment of the enzyme inside a water-insoluble polymer lattice or semi-permeable membrane

Advantages of Enzyme Immobilization

(1) Enzymes being quite expensive and also having the unique ability to be used repeatedly only in a situation when these may be recovered completely from the accomplished reaction mixtures. In true sense, immobilization distinctly and specifically allows their repeated usage by virtue of the fact that such enzyme preparation may be separated conveniently from the reaction system involved.

(2)     Importantly, the final desired product should be readily from the enzyme. It goes a long way in affecting reduction and saving upon the cost of ‘downstream processing’ of the ensuing end-product.

(3)     Non-aqueous systems (i.e., using organic solvents exclusively) are found to be fairly compatible with the immobilized enzymes particularly, and this may be regarded to be extremely desirable in certain typical and specific instances.

(4)     Immobilized enzymes may be used predominantly in most continuous production systems; and, of course, this not absolutely feasible and possible with the ‘free-enzymes’.

(5)     Immobilized enzymes, a few selected ones, may exhibit thermo stability of the highest order, viz., the free-enzyme glucose isomerase usually gets denatured only at 45°C in solution ; however, when immobilized suitably the enzyme is found to be stable enough up to 1 year at 65°C.

(6)     Importantly, the ultimate recovery of ‘immobilized enzyme’ would drastically minimize the high effluent disposable problems (which is quite acute in several fermentation industries).

(7) Immobilized enzymes may be employed at a much higher concentration range in comparison to the corresponding free enzyme.

Disadvantages of Enzyme Immobilization

Immobilized enzymes do offer several disadvantages which are briefly discussed in the section that follows:

(1) Enzyme immobilization evidently gives rise to an additional bearing on cost. Hence, this improved technique is got to be used only in such an event when there prevails a sound economic viability, feasibility, safety, and above all a positive edge over the corresponding ‘soluble enzymes’.

(2)             Immobilization of enzymes invariably affects the stability and or activity adversely. In order to circumvent such typical instances one may have to adhere strictly to the laid down developed immobilization protocols

(3)            Practical utilization of the ‘immobilized enzymes’ may not prove to be of any use or advantage when one of the substrates is found to be insoluble.

(4)             Certain immobilization protocols do offer a good number of serious problems with respect to the diffusion of the ensuing substrate to have an access to the corresponding enzyme.

Tumor suppressor gene

Tumor suppressor gene

Introduction

A tumor suppressor gene, or anti-oncogene, is a gene that protects a cell from one step on the path to cancer. When this gene is mutated to cause a loss or reduction in its function, the cell can progress to cancer, usually in combination with other genetic changes.

Two-hit hypothesis

Unlike oncogenes, tumor suppressor genes generally follow the 'two-hit hypothesis', which implies that both alleles that code for a particular gene must be affected before an effect is manifested. This is due to the fact that if only one allele for the gene is damaged, the second can still produce the correct protein. In other words, mutant tumor suppressor’s alleles are usually recessive whereas mutant oncogene alleles are typically dominant. The two-hit hypothesis was first proposed by A.G. Knudson for cases of retinoblastoma. Knudson observed that the age of onset of retinoblastoma followed 2nd order kinetics, implying that two independent genetic events were necessary. He recognized that this was consistent with a recessive mutation involving a single gene, but requiring biallelic mutation. Oncogene mutations, in contrast, generally involve a single allele because they are gain of function mutations. There are notable exceptions to the 'two-hit' rule for tumor suppressors, such as certain mutations in the p53 gene product. p53 mutations can function as a 'dominant negative', meaning that a mutated p53 protein can prevent the function of normal protein from the un-mutated allele. Other tumor-suppressor genes that are exceptions to the 'two-hit' rule are those which exhibit haploinsufficiency. An example of this is the p27Kip1 cell-cycle inhibitor, in which mutation of a single allele causes increased carcinogen susceptibility.

Functions

Tumor-suppressor genes, or more precisely, the proteins for which they code, either have a dampening or repressive effect on the regulation of the cell cycle or promote apoptosis, and sometimes do both. The functions of tumor-suppressor proteins fall into several categories including the following:

1. Repression of genesthat is essential for the continuing of the cell cycle. If these genes are not expressed, the cell cycle will not continue, effectively inhibiting cell division.
2. Coupling the cell cycle to DNA damage. As long as there is damaged DNA in the cell, it should not divide. If the damage can be repaired, the cell cycle can continue.
3. If the damage cannot be repaired, the cell should initiate apoptosis (programmed cell death) to remove the threat it poses for the greater good of the organism.
4. Some proteins involved in cell adhesion prevent tumor cells from dispersing, block loss of contact inhibition, and inhibit metastasis. These proteins are known as metastasis suppressors.

Examples

The first tumor-suppressor protein discovered was the Retinoblastoma protein (pRb) in human retinoblastoma; however, recent evidence has also implicated pRb as a tumor-survival factor.

Another important tumor suppressor is the p53 tumor-suppressor protein encoded by the TP53 gene. Homozygous loss of p53 is found in 70% of colon cancers, 30–50% of breast cancers, and 50% of lung cancers. Mutated p53 is also involved in the pathophysiology of leukemias, lymphomas, sarcomas, and neurogenic tumors. Abnormalities of the p53 gene can be inherited in Li-Fraumeni syndrome (LFS), which increases the risk of developing various types of cancers.

PTEN acts by opposing the action of PI3K, which is essential for anti-apoptotic, pro-tumorogenicAktactivation. Other examples of tumor suppressors include APC and CD95.

Protein 53 or tumor protein 53 (p53)

Protein 53 or tumor protein 53 (p53)

Introduction

p53 (also known as protein 53 or tumor protein 53), is a transcription factor that in humans is encoded by the TP53 gene.  p53 is important in multicellular organisms, where it regulates the cell cycle and thus functions as a tumor suppressor that is involved in preventing cancer. As such, p53 has been described as "the guardian of the genome," "the guardian angel gene," and the "master watchman," referring to its role in conserving stability by preventing genome mutation.

An outline of possible p53 actions with normal and damaged cells

p53 was identified in 1979 by Lionel Crawford, David P. Lane, Arnold Levine, and Lloyd Old. It had been hypothesized to exist before as the target of the SV40 virus, a strain that induced development of tumors. The TP53 gene from the mouse was first cloned by Peter Chumakov of the Russian Academy of Sciences in 1982, and independently in 1983 by Moshe Oren (Weizmann Institute). The human TP53 gene was cloned in 1984.

It was initially presumed to be an oncogene due to the use of mutated cDNA following purification of tumor cell mRNA. Its character as a tumor suppressor gene was finally revealed in 1989 by Bert Vogelstein working at Johns Hopkins School of Medicine.

The name p53 is in reference to its apparent molecular mass: it runs as a 53 kilodalton (kDa) protein on SDS-PAGE. But based on calculations from its amino acid residues, p53's mass is actually only 43.7kDa. This difference is due to the high number of proline residues in the protein which slow its migration on SDS-PAGE, thus making it appear heavier than it actually is. This effect is observed with p53 from a variety of species, including humans, rodents, frogs, and fish.

Nomenclature

p53 is also known as:

• UniProt name: Cellular tumor antigen p53
• Antigen NY-CO-13
• Phosphoprotein p53
• Transformation-related protein 53 (TRP53)
• Tumor suppressor p53

Structure

Human p53 is a nuclear phosphoprotein of MW 53 kDa, encoded by a 20-Kb gene containing 11 exons and 10 introns, which is located on the small arm of chromosome 17. 

This gene belongs to a highly conserved gene family containing at least two other members, p63 and p73. Although these proteins are structurally and functionally related to each other, p53 seems to have evolved in higher organisms to prevent tumor development, whereas p63 and p73 have clear roles in normal developmental biology

Wild-type p53 protein contains 393 amino acids and is composed of several structural and functional domains (as shown in figure):

Figure: Schematic representation of the p53 structure. p53 contains 393 amino acids, consisting of three functional domains, i.e. an Nterminal activation domain, DNA binding domain and C-terminal tetramerization domain. The N-terminal domain includes transactivation subdomain and a PXXP region that is a proline-rich fragment. The central DNA binding domain is required for sequence-specific DNA binding and amino acid residues within this domain are frequently mutated in human cancer cells and tumor tissues. The Arg175, Gly245, Arg248, Arg249, Arg273, and Arg282 are reported to be mutation hot spots in various human cancers. The C-terminal region is considered to perform a regulatory function. Residues on this basic C-terminal domain undergo posttranslational modifications including phosphorylation and acetylation.

 NLS, nuclear localization signal sequence; NES, nuclear export signal sequence.

v  An N-terminus containing an amino-terminal domain (residues 1-42)

v  A proline-rich region with multiple copies of the PXXP sequence (residues 61-94, where X is any amino acid),

v  A central core domain (residues 102-292),

v  A C terminal region (residues 301-393) containing an oligomerization domain (residues 324-355),

v  A strongly basic carboxyl terminal regulatory domain (residues 363-393), a nuclear localization signal sequence and 3 nuclear export signal sequence.

v  The amino-terminal domain is required for transactivation activity and interacts with various transcription factors including acetyltransferases and MDM2 (murine double minute 2, which in humans is identified as Hdm2).

v  The proline-rich region plays a role in p53 stability regulated by MDM2, wherein p53 becomes more susceptible to degradation by MDM2 if this region is deleted. The central core of this protein is made up primarily of the DNA-binding domain required for sequence-specific DNA binding (the consensus sequence contains two copies of the 10-bp motif 5’-PuPuPuC(A/T)-(T/A)GPyPyPy-3’, separated by 0-13 bp).

v  The basic C-terminus of p53 also functions as a negative regulatory domain,and has also been implicated in induction of cell death. According to the allosteric model, in which C-terminal tail of p53 was considered as a negative regulator and may regulate the ability of its core DNA binding domain to lock the DNA binding domain as a latent conformation.

v  Structural studies of p53 have revealed that the majority of p53 mutations found in cancers are missense mutations that are mostly located in the central DNA-binding domain, and more than 80% of p53 mutation studies have focused on residues between 126–306.

v  In the p53 family, both p73 and p63 show considerable homology with p53 and have similar domain structures including an oligomerization domain, with over 60% amino acid identity within the DNA binding region, and all three of these proteins can induce apoptosis. However, at the same time there are many structural and functional differences between p53 and its other two family members.

Function

In its anti-cancer role, p53 works through several mechanisms:

• It can activate DNA repair proteins when DNA has sustained damage.
• It can induce growth arrest by holding the cell cycle at the G₁/S regulation point on DNA damage recognition (if it holds the cell here for long enough, the DNA repair proteins will have time to fix the damage and the cell will be allowed to continue the cell cycle.)
• It can initiate apoptosis, the programmed cell death, if the DNA damage proves to be irreparable.

·         p53 is essential for preventing inappropriate cell proliferation and maintaining genome integrity.

·         p53 activation involves an increase in overall p53 protein level as well as qualitative changes in the protein through extensive posttranslational modification, thus resulting in activation of p53-targeted genes.

·         Many of the multiple functions of p53 including the primary role of p53 in tumor suppression, can be attributed to its ability to act as a sequence-specific transcription factor which regulates expression of different cellular genes to modulate various cellular processes, although protein-protein interactions may also play a role. In response to various types of stress, p53 is accumulated in the nucleus and binds to specific sites in the regulatory regions of p53- responsive genes, and then strongly promotes the transcription of such genes.

·          The functions of p53 target genes are diverse, corresponding to p53’s activity as a multifunctional protein.

Retinoblastoma protein (pRb or Rb)

Retinoblastoma protein (pRb or Rb)

Introduction

The retinoblastoma protein (abbreviated pRb or Rb) is a tumor suppressor protein that is dysfunctional in many types of cancer.  One highly studied function of pRb is to prevent excessive cell growth by inhibiting cell cycle progression until a cell is ready to divide.

pRb belongs to the pocket protein family, whose members have a pocket for the functional binding of other proteins. Should an oncogenic protein, such as those produced by cells infected by high-risk types of human papillomaviruses, bind and inactivate pRb, this can lead to cancer.

Name and genetics

In humans, the protein is encoded by the RB1 gene located on 13q14.1-q14.2. If both alleles of this gene are mutated early in life, the protein is inactivated and results in development of retinoblastoma cancer, hence the name Rb. It is not known why an eye cancer results from a mutation in a gene that is important all over the body.

Two forms of retinoblastoma were noticed: a bilateral, familial form and a unilateral, sporadic form. Sufferers of the former were 6 times more likely to develop other types of cancer later in life. This highlighted the fact that mutated Rb could be inherited and lent support to the two-hit hypothesis. This states that only one working allele of a tumor suppressor gene is necessary for its function (the mutated gene is recessive), and so both need to be mutated before the cancer phenotype will appear. In the familial form, a mutated allele is inherited along with a normal allele. In this case, should a cell sustain only one mutation in the other RB gene, all pRb in that cell would be ineffective at inhibiting cell cycle progression, allowing cells to divide uncontrollably and eventually become cancerous. Furthermore, as one allele is already mutated in all other somatic cells, the future incidence of cancers in these individuals is observed with linear kinetics. The working allele need not undergo a mutation per se, as loss of heterozygosity (LOH) is frequently observed in such tumors.

However, in the sporadic form, both alleles would need to sustain a mutation before the cell can become cancerous. This explains why sufferers of sporadic retinoblastoma are not at increased risk of cancers later in life, as both alleles are functional in all their other cells. Future cancer incidence in sporadic Rb cases is observed with polynomial kinetics, not exactly quadratic as expected because the first mutation must arise through normal mechanisms, and then can be duplicated by LOH to result in a tumor progenitor.

Evaluation of depilatories (IS: 9636-1988)

Evaluation of depilatories (IS: 9636-1988)

This standard prescribes requirement & methods of sampling & test for chemical depilatories having alkaline thioglycollic composition. This standard does not cover depilatories having metallic sulphides & stannites composition.

Requirements are: The depilatories should be in the form of cream or lotion. It should be colorless & shall not emit foul smell & acceptable chemical depilatories formulation should follow the following attributes:

a.) It should convert human hair completely in about 10 minute to a soft plastic mass which may be easily removed from skin by wiping or rinsing.

b.)It should be non-toxic on skin even on long contact.

c.) It should be easily applied, cosmetically elegant & pleasantly perfumed.

d.)It should be stain free on clothing.

e.) All the raw material used shall confirmed respective Indian standard specification.

f.) Depilatories are in the form cream & lotion having thioglycollic acid composition shall compiles with following requirements

i.)        pH range should be 11-12.7

ii.)       Presence of calcium thioglycollate, calculated as thioglycollic acid present by mass (2.5-5%)

iii.)      thermal stability: it should be passed test for thermal stability

g.) material should be packed well closed container & lacquers (aluminum collapsible tube)

On the label

The following instructions shall be on container or leaflet supplied with the pack

a.) Never use the material inflame or broken or near eyes

b.) Should this occur, wash with lukewarm water (cold water)

c.)  If used for first time, carry out the following test: used a little hair remover over 5 cm² of skin on inner elbow. If 24 hours later if skin is normal, material may be safely used.

Determination of pH

A pH meter is required which is equipped with glass electrode. pH shall be determined directly in case of cream or lotion using pH meter with a glass electrode.

Determination of calcium thioglycollate

Reagents required: Conc. HCl, standard I₂ solution (0.1 N), and starch as indicator 0.5% w/v.

Procedure: accurately weighed about 5 gram of sample in a 250 ml conical flask. Add about 75 ml of water & 15 ml of conc. HCl. Heat on water bath for 10 minutes. Cool & titrate with iodine solution using starch solution as indicator.

Calculation: calculate on the basis each ml of 0.1 N solution of iodine equivalent to 0.00921 gm of thioglycollic acid.

Thermal stability

Fill a clear glass round bottle of about 45 ml overflow capacity with the material & closed tightly. Heat the bottle at 37± 1^oC for 16 hours. Material shall be considered pass the test no separation is observed.