Kinetics of the Reaction of Renin with Nine Synthetic Peptide Substrates

A number of peptides have been synthesized which represent portions of the tetradecapeptide renin substrate molecule, and which contain the hydrolyzable leu-leu bond. An automatic chemical method for determination of the velocity of the reaction of renin with these compounds was developed. Application of the method at several levels of substrate concentration permitted construction of Lineweaver-Burk plots, and calculation of Michaelis constants (K(m)) and maximal velocities (V(max)). The results show that the maximum affinity of the enzyme (lowest K(m)) for substrate is achieved only with the full tetradecapeptide molecule (asp(1)-arg(2)-val(3)-tyr(4)-ileu(5)-his(6)-pro(7)-phe(8)-his(9)-leu(10)-leu(11)-val(12)-tyr(13)-ser(14)). Removal of asp(1) and arg(2) from the N-terminal increases the K(m) eight-fold. Further, moderate increase in K(m) occurs when the next amino acids, val(3), tyr(4) and ileu(5), are removed. The further removal of his(6) results in a marked reduction in the V(max). Removal of ser(14) from the C-terminal of the nonapeptide his(6)-pro(7)-phe(8)-his(9)-leu(10)-leu(11)-val(12)-tyr(13)-ser(14) does not greatly affect the K(m) nor the V(max). Further removal of tyr(13) from this compound results in complete loss of substrate activity. It is suggested that the compounds his(6)-pro(7)-phe(8)-his(9)-leu(10)-leu(11)-val(12)-tyr(13)-ser(14) or his(6)-pro(7)-phe(8)-his(9)-leu(10)-leu(11)-val(12)-tyr(13) might be used as substrates for the chemical assay and standardization of renin.