Hafkenscheid J C, Dijt C C
Clin Chem. 1979 Jan;25(1):55-9.
To investigate the activation of aspartate- and alanine aminotransferases by pyridoxal-5'-phosphate, we determined the enzymatic activity in serum in two different ways: (a) Preincubation of the serum alone or the serum with pyridoxal-5'-phosphate and starting the reaction by the addition of the serum sample or the serum sample + coenzyme, respectively. (b) Preincubation of the serum or the serum with pyridoxal-5'-phosphate in the reaction medium and starting the reaction by adding 2-oxoglutarate. There are only small differences in activities of both aminotransferases determined according to these two different methods. The stimulation by pyridoxal-5'-phosphate is also of the same order, when both methods are compared. Further, these enzymatic activities were measured with use of various concentrations of substrates. From our experiments we conclude that the degree of stimulation of the apoenzyme of the two enzymes is independent of which way the enzymatic reaction is carried out or the substrate concentration, except that aspartate aminotransferase activity is more stimulated by the coenzyme at higher 2-oxoglutarate concentrations.
为了研究磷酸吡哆醛对天冬氨酸转氨酶和丙氨酸转氨酶的激活作用，我们用两种不同的方法测定了血清中的酶活性：(a) 单独预孵育血清，或血清与磷酸吡哆醛预孵育，然后分别加入血清样本或血清样本+辅酶来启动反应。(b) 在反应介质中预孵育血清或血清与磷酸吡哆醛，然后加入2-氧代戊二酸来启动反应。根据这两种不同方法测定的两种转氨酶的活性仅有微小差异。比较这两种方法时，磷酸吡哆醛的刺激作用也处于同一水平。此外，使用不同浓度的底物测量了这些酶活性。从我们的实验中我们得出结论，两种酶的脱辅酶的刺激程度与酶促反应的进行方式或底物浓度无关，只是在较高的2-氧代戊二酸浓度下，辅酶对天冬氨酸转氨酶活性的刺激作用更强。
