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INSULIN : Structure Computer-generated image of six insulin molecules assembled in a hexamer, highlighting the threefold symmetry, the zinc ions holding it together, and the histidine residues involved in zinc binding. Insulin is stored in the body as a hexamer, while the active form is the monomer.
SOURCES OF ANIMAL INSULIN Best sources : Cow and Pig Very small difference in the Pig -1 amino acid variation in B30 Cow insulin has two differences A8 and B30
Why Cow and Pig? Bovine Insulin Easy availability from slaughter houses Chicken and duck have 7 and 6 amino acid differences as compared to human insulin Hence, wouldn’t be good choices
Marketed product The first of these molecules to be marketed - called insulin lispro - is engineered such that lysine and proline resting on the C-terminal end of the B chain are reversed; this modification does not alter receptor binding, but minimizes the tendency to form dimmers and hexamers.
Importance of similarity The primary sequence of amino acids influences the tertiary structure of protein Hence, it’s possible that a change in the protein sequence could alter the tertiary structure Resulting in a different shape .
PI value of INSULIN The pi value for all animal insulins would be similar to human insulin (except for chicken and duck) This is because, amino acid changes all involved neutral amino acids. Chicken insulin would be more basic whereas duck would be more acidic.
The amino acid sequence for insulin is almost the same in different mammals. Porcine insulin has only a single amino acid variation from the human variety, and bovine insulin varies by two amino acids. Both are active on the human receptor with approximately the same strength. Prior to the introduction of biosynthetic human insulin, insulin derived from sharks was widely used in Japan. Even insulin from some species of fish may be effective in humans. Non-human insulins can cause allergic reactions in a tiny number of people, as can genetically engineered "human" insulin
SDS-PAGE Electrophoresis ofInsulin and Proinsulin :-
OBSERVATIONS Proinsulin is a single stranded polypeptide with 3 intra-molecular disuphide bonds. Insulin is double-stranded polupeptide with 2 intermolecular and 1 intramolecular. In that case, there will be numerous A and B strands in solution and correct system AB system residue must find each other in solution before an intramolecular disulphide bond forms.
Insulin OVER Proinsulin! When insulin was originally purified from bovine or porcine pancreas, all the proinsulin was not fully removed. When some people used these insulins, the proinsulin may have caused the body to react with a rash, to resist the insulin, or even to make dents or lumps in the skin at the place where the insulin was injected.