Properties of Rhizopus sp. Glucoamylase Polymerized by Crosslinking with Glutaraldehyde

概要

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A major glucoamylase [EC 3.2.1.3] from a Rhizopus sp., Gluc_1,was polymerized by crosslinking with glutaraldehyde. The polymerized Gluc_1 (named poly-Gluc_1) showed a drastic decrease (55%) in lysine content as well as a slight decrease (11%) in tyrosine content as compared with Gluc_1 and had an apparent molecular weight higher than 10^6 daltons as estimated by gel filtration on Sepharose 6B. The circular dichroism spectrum, together with the ultraviolet and fluorescence spectra, indicated that poly-Gluc_1 was different from Gluc_1 not only in the states of aromatic amino acid side chains but also in the protein backbone conformation. The stabilities of poly-Gluc_1 to pH and heat were not enhanced appreciably as compared with those of Gluc_1,though the heat stability showed a slight enhancement at 40-45℃ followed by a sharper decline at higher temperatures. For low-molecular-weight substrates, poly-Gluc_1 had similar kinetic parameters and activities to those of Gluc_1,whereas for high-molecular-weight substrates, poly-Gluc_1 showed 2-10 times higher K_m and 2-4.5 times lower V_<max> values and thus 2-4.5 times lower activities. Poly-Gluc_1 exhibited 25 times lower activity than Gluc_1 towards raw starch but was still tightly bound to it, suggesting that the lysine residues are not involved in the binding to raw starch.
社団法人日本薬学会の論文
1986-02-25