Tunnicliff G, Ngo T T, Rojo-Ortega J M, Barbeau A
Can J Biochem. 1977 Apr;55(4):479-84. doi: 10.1139/o77-067.
Cytoplasmic-mitochondria-enriched and synaptosome-enriched subcellular fractions were prepared from rat brain to study certain kinetic properties of gamma-aminobutyrate: alpha-oxoglutarate aminotransferase (GABA-T) (EC 2.6.1.19) from each of the sources. From this study two differences emerged. Firstly, the cytoplasmic enzyme exhibited an eightfold greater affinity for gamma-aminobutyric acid (GABA) than did the synaptosomal GABA-T; the Km being 6.5 mM and 53 mM, respectively. Secondly, synaptosomal GABA-T is comparatively more susceptible to inhibition by the substrate analogues 2,4-diaminobutyric acid (DABA) and aminooxyacetic acid (AOAA) than is the enzyme from the cytoplasmic mitochondrial fraction. In each case the inhibition was of a competitive nature with respect to GABA. The Ki for the DABA was 13 mM for the cytoplasmic-derived enzyme and 8mM for the synaptosomal enzyme. With AOAA the Ki was 0.1 muM and 0.06 muM for the synaptosomal and cytoplasmic mitochondrial enzyme, respectively. These results provide further evidence that GABA-T from cytoplasmic mitochondria is different in several respects from the enzyme found in synaptosomes.
从大鼠脑中制备富含细胞质线粒体和富含突触体的亚细胞组分，以研究来自每种来源的γ-氨基丁酸：α-酮戊二酸转氨酶（GABA-T）（EC 2.6.1.19）的某些动力学特性。从这项研究中出现了两个差异。首先，细胞质酶对γ-氨基丁酸（GABA）的亲和力比突触体GABA-T高八倍；Km分别为6.5 mM和53 mM。其次，与来自细胞质线粒体组分的酶相比，突触体GABA-T相对更容易受到底物类似物2,4-二氨基丁酸（DABA）和氨基氧乙酸（AOAA）的抑制。在每种情况下，抑制作用相对于GABA都是竞争性的。细胞质来源的酶对DABA的Ki为13 mM，突触体酶为8 mM。对于AOAA，突触体和细胞质线粒体酶的Ki分别为0.1 μM和0.06 μM。这些结果进一步证明，细胞质线粒体中的GABA-T在几个方面与突触体中的酶不同。
