β-淀粉酶抗性直链淀粉。尿素对β-淀粉酶有限水解直链淀粉的影响。
Beta-amylase-resistant amylose. Effect of urea on the limited hydrolysis of amylose by beta-amylase.
作者信息
Patil N B
出版信息
Biochem J. 1976 Feb 1;153(2):339-42. doi: 10.1042/bj1530339.
Amylose prepared from starch dispersed in 10M-urea, pH6.2, was found to be resistant to the action of beta-amylase and phosphorylase, though it was degraded by alpha-amylase. Amylose isolated by conventional methods was similarly refractory after urea treatment, and was hydrolysed by beta-amylase to the extent of 32-35%; it had no inhibitory effect towards beta-amylase. The physical and chemical properties of the modified amylose were in general comparable with those of normal amylose with a beta-amylolysis limit of 94-98%. Starch and amylopectin were unaffected by urea treatment, i.e. the presence of amylopectin protected amylose against changes induced in it by urea. It is speculated that urea treatment "freezes" amylose molecules in a conformation that renders non-reducing termini inaccessible to the active site of the exo-enzymes. Such changes may limit the degradative action of beta-amylase and phosphorylase.
从分散于pH6.2的10M尿素中的淀粉制备的直链淀粉，虽能被α-淀粉酶降解，但对β-淀粉酶和磷酸化酶的作用具有抗性。用常规方法分离的直链淀粉经尿素处理后同样具有抗性，并且能被β-淀粉酶水解32% - 35%；它对β-淀粉酶没有抑制作用。改性直链淀粉的物理和化学性质总体上与β-淀粉酶解极限为94% - 98%的正常直链淀粉相当。淀粉和支链淀粉不受尿素处理的影响，即支链淀粉的存在保护直链淀粉免受尿素诱导的变化。据推测，尿素处理将直链淀粉分子“冻结”在一种构象中，使外切酶的活性位点无法接近非还原末端。这种变化可能会限制β-淀粉酶和磷酸化酶的降解作用。
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