MALEYLATION AND PH-DEPENDENCE OF STREPTOMYCES GRISEUS PROTEASE B

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Abstract
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.