【摘要】 红曲霉（Monascus sp.）As 3.3491的葡萄糖淀粉酶具有多型性,其中的两个主要组分 E₃和 E₄得到了凝胶电泳均一的样品。比较了它们的底物特异性,同时与粗酶液和未分纯的 E₃₊₄作了比较。从酶对底物的分解限度来看,粗酶液能100%的分解可溶性淀粉、直链淀粉、支链淀粉、糖原、玉米淀粉、马铃薯淀粉、麦芽糖和麦芽三糖,也能分解茁霉多糖（Pullulan）（35.8%）,潘糖（Panose6-α-葡糖基麦芽糖）（27.3%）、异麦芽糖（9.6%）、右旋糖酐（5%）、龙胆二糖（1.9%）。纯北的 E₃和 E₄仅能100%地分解糖原,麦芽糖和麦芽三糖,对其他底物的分解限度则有不同程度的降低,E₃,E₄和 E₃₊₄之间没有明显差别,可以看出粗酶液中有能分解α-1,6-糖苷键的酶存在。各种酶样品均不能分解环状糊精（α,β和γ）,纤维二糖、龙胆二糖和（?）糖。比较了各种酶样品对不同底物包括不同平均链长的糊精的反应初速度,在用同样的百分浓度下,对麦芽糖、麦芽三糖、支链淀粉,可溶性淀粉等的反应初速度高,而对直链淀粉的反应初速度要低得多,这与它没有分枝,非还原性末端较少有关。对不同平均链长的小分子糊精的反应初速度随着链长的增加而增加。而对异麦芽糖的水解速度仅相当于麦芽糖的1%左右,E₃,E₄和 E₃₊₄之间无明显的差别。用麦芽糖和可溶性淀粉为底物,比较了 E₃和 E₄的 K_m 值和 V_max值。两种酶对麦芽糖的K_m 值均为1.38×10^-1（%）,对于可溶性淀粉的 K_m 值均为1.05（%）,V_max也基本相同。E₃和 E₄对可溶性淀粉的水解产物均为β-葡萄糖,两种酶均能催化葡萄糖合成少量寡糖。更多还原

【Abstract】 Substrate specificity of the two formsof glucoamylase E₃ and E₄ was examinedand compared with the crude enzyme andan unpurified sample of E₃₊₄ with thefollowing results:1.Degree of HydrolysisThe crude enzyme hydrolyzed solublestarch,amylose,amylopectin,glycogen,corn starch,potato starch,maltose,andmaltotriose to 100%,and partially hydro-lyzed pullulan （35.8%）,panose （27.3%）,iso-maltose （9.6%）,dextran （5%） andgentiobiose （1.7%）,The pure enzymes E₃and E₄ hydrolyzed only glycogen,maltoseand maltotriose to 100%.The degree ofHydrolysis of other substrates weresomewhat lowered,which suggests the pre-sence of other enzymes capable of hy-drolyzing α-（1-6） glucosidic linkages inthe crude enzyme.There was no apparentdifference between E₃ and E₄ and E₃₊₄.None of the four preparations can attackcyelo-dextrins （α,β,γ）,cellobiose,gen-tiobiose and trehalose.2.Initial Rate of ReactionThe initial rates of hydrolysis ofmaltose,maltotriose,amylopectin andsoluble starch were much higher than thatof amylose,which is consistent with itslinear structure and deficient in nonredu-cing ends.The initial rates of hydrolysisof oligo-dextrins were increased with theincrease of chain length of the dextrins.Isomaltose was hydrolyzed at an ini-tial rate 100 times slower than maltose.No difference was exists between E₃ andE₄.3.K_m and V_max valuesThe K_m values of E₃ and E₄ for mal-tose (1.38×10^-1%) and soluble starch（1.05%） were similar and the V_max valuesalso similar.Both E₃ and E₄ hydrolyzed starch toβ-glucose.In concentrated glucose solu-tion,reversible synthesis of oligosacchari-de was observed.更多还原