Proteolytic Modification of a Glucoamylase from a Rhizopus sp.
1983 年 31 巻 3 号 p. 1001-1009
詳細
1983 年 31 巻 3 号 p. 1001-1009
Three forms of glucoamylase [EC 3.2.1.3] have been purified from a Rhizopus sp. and named Gluc1, Gluc2 and Gluc3 in order of content (T. Takahashi et al., J. Biochem., 84, 1183 (1978)). Gluc1 (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 Gluc1 but their N-terminal amino acids were different from that of Gluc1. 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 Gluc1. The two modified enzymes had almost the same pH optimum, pH stability and heat stability as those of Gluc1. However, they differed from Gluc1 in the values of Km and Vmax for high-molecular-weight substrates, although they showed identical kinetic parameters for low-molecular-weight substrates. The close similarity between pap-Gluc and Gluc2 as well as between chymo-Gluc and Gluc3 is discussed.
