Action of Trypsin on Synthetic Substrates

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Abstract
A study was carried out to determine why the Arg-Gly bond in oxidized B-chain of insulin is hydrolyzed more rapidly by trypsin [EC 3.4.21.4, formerly 3.4.4.4] than the Lys-Ala bond in the same substrate. Three insulin fragments (Gly-Glu-Arg-Gly, Gly-Glu-Arg-Gly-Phe, and Thr-Pro-Lys-Ala) and a model peptide (Thr-Pro-Lys-Ala-Phe) were synthesized, and their susceptibilities to hydrolysis by trypsin were determined. No appreciable difference in susceptibility between the two tetrapeptides and the two pentapeptides, respectively, was observed. On the other hand, Gly-Glu-Arg-Gly-Phe was hydrolyzed 53 times faster than Thr-Pro-Lys-Ala. Thus, it is concluded that the difference in the lability of the two bonds in oxidized B-chain may be attributed to differences in the number of amino acid residues linked to the carboxyl groups of Arg and Lys residues.

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