Soluble, prolonged-acting insulin derivatives. I. Degree of protraction and crystallizability of insulins substituted in the termini of the B-chain

Publisher Website
Google Scholar
Abstract
Hydrophilic insulins, more positively charged than human insulin at neutral pH, have been prepared by substitution with basic amino acids at the termini of the B-chain and by blocking the C-terminal carboxyl group of the B-chain. The iso-electric pH of the insulin is thereby moved from 5.4 towards physiological levels. Slightly acid solutions of derivatives, in which charge has been added in the C-terminus of the B-chain, have a prolonged action in vivo, in particular if the carboxyl group is blocked. It is found that the prolong ed-acting hydrophilic insulins crystallize instantly when the pH is adjusted to 7. The prolonged action is ascribed to this readiness to crystallization combined with a low solubility, which may be further decreased by Increased concentration of zinc ions. Hydrophobic insulins have a prolonged action independent of the site of substitution even if the derivative is soluble at physiological pH. Some derivatives were prepared from porcine Insulin by tryptic transpeptidatlon. N-terminal B-chain substituted insulins were prepared by alkylation of a biosynthetic single-chain insulin precursor, followed by tryptic transpeptidation rendering the double chain insulin derivative. The observed blood glucose lowering in the rabbits implies that neither N- nor C-terminal B-chain substitution results in substantial deterioration of biological potency. An index for the degree of protraction based on the blood glucose data is used to compare the insulins.