Amino acids and peptides. XV. Synthesis of Gln-Val-Val-Ala-Gly and derivatives, a common sequence of thiol proteinase inhibitors and their effects on thiol proteinase.

The Gln-Val-Val-Ala-Gly sequence, which occurs frequently in several natural thiol proteinase inhibitors, and derivatives were synthesized by conventional solution methods and their effect on thiol proteinases were examined. The studies led us to the conclusion that certain of these peptides exhibited a weak inhibitory effect on the thiol proteinase, papain. One of them, Z-Gln-Val-Val-Ala-Gly-OMe, showed a protective effect on papain from natural thiol proteinase inhibitor-induced inactivation. The relationship between structure and activity of these derivatives was studied and certain conclusions were derived on possible mode of action of these inhibitors. From these studies, it was concluded that Z-Gln-Val-Val-OMe was the smallest peptide to exhibit some effect on papain.