Nakano K, Fukui T
J Biol Chem. 1986 Jun 25;261(18):8230-6.
The complete amino acid sequence of potato alpha-glucan phosphorylase has been determined. The monomer contains 916 amino acids with a molecular weight of 103,916. About one-fourth of the amino-terminal threonine is blocked by an acetyl group. Sequence comparison among phosphorylases from potato tuber, rabbit muscle, and Escherichia coli reveals the presence of a characteristic 78-residue insertion in the middle of the polypeptide chain of the potato enzyme. Except for the large inserted portion, 51 and 40% of the amino acids in the potato enzyme are identical with the rabbit muscle and E. coli enzymes, respectively. The regions relevant to the regulation of activity are completely different among the three enzymes, whereas those involved in the catalytic reaction are well conserved. The potato enzyme sequence is consistent with the tertiary structure of the rabbit muscle enzyme. The 78-residue insertion is located at the junction of the amino- and carboxyl-terminal domains on the molecular surface near the glycogen storage site. This insertion could account for the substrate discrimination of the potato enzyme. The molecular evolution of phosphorylase is discussed based on the presence of the large insertion of the potato enzyme.
马铃薯α-葡聚糖磷酸化酶的完整氨基酸序列已被确定。该单体含有916个氨基酸，分子量为103,916。氨基末端的苏氨酸约四分之一被乙酰基封闭。对来自马铃薯块茎、兔肌肉和大肠杆菌的磷酸化酶进行序列比较，发现在马铃薯酶的多肽链中部存在一个由78个残基组成的特征性插入片段。除了这个大的插入部分外，马铃薯酶中分别有51%和40%的氨基酸与兔肌肉酶和大肠杆菌酶相同。三种酶中与活性调节相关的区域完全不同，而参与催化反应的区域则高度保守。马铃薯酶的序列与兔肌肉酶的三级结构一致。这个由78个残基组成的插入片段位于分子表面靠近糖原储存位点的氨基末端和羧基末端结构域的交界处。这种插入可能解释了马铃薯酶对底物的选择性。基于马铃薯酶存在大的插入片段，对磷酸化酶的分子进化进行了讨论。
