Bezirdzhian Kh O, Kocharian Sh M, Akopian Zh I
Biokhimiia. 1986 Jul;51(7):1085-92.
The presence of two forms (high and low molecular weight ones) of purine nucleoside phosphorylase II (purine nucleoside: orthophosphate ribosyltransferase, EC 2.4.2.1) was demonstrated. The high molecular weight form of the enzyme was purified, and the properties of both forms were compared. The enzyme forms were shown to differ in their quaternary structure (trimeric and hexameric), molecular weight of the native enzyme and its subunits (85,000 and 28,000 for the trimer, 150,000 and 25,000 for the hexamer, respectively) as well as substrate specificity (the trimer is specific for all major purine nucleosides, while the hexamer does not cleave adenine nucleosides). Adenosine is a competitive inhibitor of the hexameric form with respect to deoxyguanosine (Ki = 1.16 X 10(-3) M); the Km value for deoxyguanosine is 9.85 X 10(-5) M. The isoelectric point for the both forms of the enzyme in the presence of 9 M urea is about 5.5. Both forms have a pH optimum of phosphorolytic activity between 6.5 and 7.0.
已证实存在嘌呤核苷磷酸化酶II（嘌呤核苷：正磷酸核糖基转移酶，EC 2.4.2.1）的两种形式（高分子量和低分子量形式）。纯化了该酶的高分子量形式，并比较了两种形式的性质。结果表明，这两种酶形式在四级结构（三聚体和六聚体）、天然酶及其亚基的分子量（三聚体分别为85,000和28,000，六聚体分别为150,000和25,000）以及底物特异性（三聚体对所有主要嘌呤核苷具有特异性，而六聚体不切割腺嘌呤核苷）方面存在差异。腺苷是六聚体形式相对于脱氧鸟苷的竞争性抑制剂（Ki = 1.16×10^(-3) M）；脱氧鸟苷的Km值为9.85×10^(-5) M。在9 M尿素存在下，两种酶形式的等电点约为5.5。两种形式的磷酸解活性的最适pH均在6.5至7.0之间。
