Taniguchi N, Meister A
J Biol Chem. 1978 Mar 25;253(6):1799-806.
gamma-Glutamyl cyclotransferase, highly purified from rat kidney, contains several readily accessible sulfhydryl groups whose modification appears to be associated with the appearance of multiple enzyme forms as determined by isoelectric focusing and ion exchange chromatography. The enzyme was obtained in a 1000-fold purified and apparently homogeneous form by a procedures involving treatment with dithiothreitol followed by chromatography on thiol-Sepharose. The enzyme was also isolated in a highly active, apparently homogeneous, and stable form after reduction and treatment with iodoacetamide. The amino acid compositions and other properties of the two forms of the enzyme were very similar. Studies on the activity of the enzyme toward a variety of gamma-glutamyl amino acids and di-gamma-glutamyl amino acids showed that the enzyme is much more active toward certain di-gamma-glutamyl amino acids than toward the corresponding gamma-glutamyl amino acids; thus, the preferred substrates have the general structure gamma-Glu-gamma-Glu-NH-R in which the nature of the R moiety has relatively little effect on activity.
γ-谷氨酰环转移酶从大鼠肾脏中高度纯化得到，含有几个易于接近的巯基，通过等电聚焦和离子交换色谱法测定，这些巯基的修饰似乎与多种酶形式的出现有关。通过包括用二硫苏糖醇处理然后在硫醇-琼脂糖上进行色谱分离的程序，以1000倍纯化且明显均一的形式获得该酶。在用碘乙酰胺还原和处理后，该酶也以高活性、明显均一且稳定的形式被分离出来。该酶两种形式的氨基酸组成和其他性质非常相似。对该酶对多种γ-谷氨酰氨基酸和二-γ-谷氨酰氨基酸活性的研究表明，该酶对某些二-γ-谷氨酰氨基酸的活性比对相应的γ-谷氨酰氨基酸的活性高得多；因此，优选的底物具有一般结构γ-Glu-γ-Glu-NH-R，其中R部分的性质对活性影响相对较小。
