Okuno E, Nakamura M, Schwarcz R
Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, 21228.
Brain Res. 1991 Mar 1;542(2):307-12. doi: 10.1016/0006-8993(91)91583-m.
Using Tris-acetate buffer rather than conventional phosphate buffer, it was possible to detect two distinct proteins capable of producing the neuroinhibitory brain metabolite kynurenic acid (KYNA) from L-kynurenine in human brain tissue. The two kynurenine aminotransferases (KATs), arbitrarily termed 'KAT I' and 'KAT II', could be physically separated by isoelectric focussing on a pH 3-10 Ampholine gradient, and, more completely, by differential elution from a DEAE-Sepharose column. KAT I showed a pronounced preference for pyruvate as a co-factor and had a pH optimum of 9.6. In contrast, KAT II was virtually equally active when either pyruvate or 2-oxoglutarate were used as the aminoacceptor, and its pH optimum was 7.4. Moreover, KAT I and KAT II differed with regard to their sensitivity to amino acids and as the aminoacceptor, and its pH optimum was 7.4. Moreover, KAT I and KAT II differed with regard to their sensitivity to amino acids and kinetic characteristics. The existence of two separate enzymes capable of producing KYNA in the human brain raises the question if and to what extent each of the enzymes regulates the cerebral synthesis of KYNA and its possible role as a modulator of excitatory amino acid receptor function.
使用Tris-醋酸盐缓冲液而非传统的磷酸盐缓冲液，能够在人脑组织中检测到两种不同的蛋白质，它们可将L-犬尿氨酸转化为具有神经抑制作用的脑代谢产物犬尿喹啉酸（KYNA）。这两种犬尿氨酸转氨酶（KATs），分别被随意命名为“KAT I”和“KAT II”，可通过在pH 3 - 10两性电解质梯度上进行等电聚焦，更彻底地通过从DEAE - 琼脂糖柱上进行差异洗脱来实现物理分离。KAT I表现出对丙酮酸作为辅因子有明显偏好，其最适pH为9.6。相比之下，当使用丙酮酸或2-氧代戊二酸作为氨基受体时，KAT II的活性几乎相同，其最适pH为7.4。此外，KAT I和KAT II在对氨基酸的敏感性以及动力学特性方面也存在差异。人脑中存在两种能够产生KYNA的不同酶，这就引发了一个问题，即每种酶是否以及在何种程度上调节大脑中KYNA的合成及其作为兴奋性氨基酸受体功能调节剂的可能作用。
