Inhibition of bovine α-chymotrypsin by cyclic trypsin inhibitor SFTI-1 isolated from sunflower seeds and its two acyclic analogues

Abstract

Trypsin inhibitor SFTI-1 isolated from sunflower seeds (comprising 14 amino acid residues and two cycles: head-to-tailcyclisation and disulfide bridge) is the smallest naturally occurring plant serine proteinase inhibitor. In our recent paperwe have shown that the elimination head-to-tail cyclisation did not change trypsin inhibitory activity as judged by measuredby association equilibrium constants Ka. The removal of disulfide bridge produced 2.4-fold lower activity. In the present paper we described chymotrypsin inhibitory activity. SFTI-1 inhibits significantly lower bovine α-chymortypsin(Ka = (5.20±1.56) × 106 M-1). The activity of the analogue with disulfide bridge only was practically the same, whereas the Ka value determined forhomodetic peptide was almost 3-fold lower. Considering the results obtained and the recent literature data we postulate thelower inhibitory activity against both enzyme of the analogue with head-to-tail cyclisation only reflect its lower proteolytic stability.