Proteolytic Modification of a Glucoamylase from a Rhizopus sp.

概要

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Three forms of glucoamylase [EC 3.2.1.3] have been purified from a Rhizopus sp. and named Gluc_1,Gluc_2 and Gluc_3 in order of content (T. Takahashi et al., J. Biochem., 84,1183 (1978)). Gluc_1 (M. W. 74000 ; specific activity 66 units/mg ; N-terminal Ala ; C-terminal-Ser-Ala・OH) was converted by papain and chymotrypsin into two active derivatives named pap-Gluc and chymo-Gluc, respectively. pap-Gluc was characterized by a molecular weight of 57000 and a specific activity of 88 units/mg, and chymo-Gluc by a molecular weight of 64000 and a specific activity of 78 units/mg. The C-terminal amino acid sequences of both modified enzymes were identical with that of Gluc_1 but their N-terminal amino acids were different from that of Gluc_1. These results, together with the results of amino acid and sugar analyses, indicate that papain and chymotrypsin liberated glycopeptide and peptide moieties, respectively, from the N-terminal side of Gluc_1. The two modified enzymes had almost the same pH optimum, pH stability and heat stability as those of Gluc_1. However, they differed from Gluc_1 in the values of K_m and V_<max> for high-molecular-weight substrates, although they showed identical kinetic parameters for low-molecular-weight substrates. The close similarity between pap-Gluc and Gluc_2 as well as between chymo-Gluc and Gluc_3 is discussed.
社団法人日本薬学会の論文
1983-03-25