Studies on the inactivation of vasoactive polypeptides by pyridoxal-5'-phosphate

The pharmacologically active peptides bradykinin (BK) lysylbradykinin or kallidin (LBK) and methionyl-lysylbradykinin (MLBK) were shown to react with pyridoxal-5'-phosphate (PLP) forming Schiff bases; upon reduction with sodium borohydride they were transformed into stable phosphopyridoxyl-kinins (PP-BK, PP-LBK and PP-MLBK). Amino acid analysis showed that the N-terminal alpha-aminogroup of the three kinins were efficiently blocked by phosphopyridoxyl groups: 98.8% for BK; 95.2% for LBK and 98.9% for MLBK. Guanidinium groups did not react with PLP. Estimated by guinea-pig ileum and the vascular permeability of rat skin assays respectively- the PP-kinins had the following average activities compared to the respective kinins: PP-BK, 0.20 and 0.16; PP-LBK, 0.05 and 0.17; PP-MLBK, 0.10 and 0.12. Isoleucyl5-angiotensin II and valyl5-angiotensin I were shown to be 50% inactivated (guinea-pig ileum assay) by reaction with PLP and reduction with borohydride.