MALEYLATION AND PH‐DEPENDENCE OF STREPTOMYCES GRISEUS PROTEASE B

The enzymatic activity of Streptomyces griseus protease B (SGPB) was measured over pH range 8.4–11.5 using a specific new, chromophoric substrate N‐succinyl‐glycyl‐glycyl‐l‐phenylalanine p‐nitroanilide. It was found that the activity is dependent on ionization of a single group with apparent pK = 10.84, possibly lysine‐125. Maleylation of the ∍‐amino group of this lysine was linearily associated with the loss of enzymatic activity. It is therefore suggested that the electrostatic interaction between the side chain of lysine‐125 and the α‐carboxyl group of the the C‐terminal tyrosine is crucial to the active conformation of the enzyme. In contrast the maleylation of the α‐amino group of the N‐terminal isoleucine was rapid but could not be correlated to the loss of activity.