Identification of the peptide bond cleaved during activation of human Clr

Abstract

CNBr cleavage of unreduced proenzyme Clr yielded fragment CP2b, isolated by gel filtration and highpressure gel permeation chromatography. This fragment (~ M _τ 55000) comprised at least 4 disulphidelinked peptides, which were separated by gel filtration after reduction and alkylation. Peptide CP2bRA4, overlapping the A‐ and B‐chain regions in proenzyme Clr was digested by V8 staphylococcal protease, and the digest separated by reversed‐phase HPLC. N‐terminal sequence analysis of peptide CP2bRA4SP9 established that Clr activation involves the cleavage of a single Arg‐Ile bond, located in the sequence:⋯ Gln‐Arg‐Gln‐Arg‐Ile‐Ile‐Gly‐Gly⋯