INSULIN : StructureComputer-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 INSULINBest sources : Cow and Pig Very small difference in the Pig -1 amino acid

variation in B30Cow insulin has two differences A8 and B30

Why Cow and Pig?

Bovine InsulinEasy availability from

slaughter housesChicken and duck have 7

and 6 amino acid differences as compared to human insulin

Hence, wouldn’t be good choices

Marketed productThe 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 similarityThe primary sequence of amino acids

influences the tertiary structure of proteinHence, 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.

Factors affecting Immune ResponseInsulin factorsPuritySpecies (bovine > pork > human)Physical properties (pH)Retarding agents (zinc, protamin, surfen)Individual factorsAgeImmunogenical background (HLA type)Presence of insulin autoantibodiesMode of insulin administrationSubcutaneous > intravenousInsulin pumpsInterrupted insulin therapy

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 of Insulin 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.