Polidoro G, Di Cola D, Di Ilio C, Politi L, Scandurra R
Mol Cell Biochem. 1976 Jun 15;11(3):155-9. doi: 10.1007/BF01744996.
Holo and apoenzyme of aspartate aminotransferase from beef kidney are 80% inactivated by photoxidation in the presence of 2 X 10(-6) M tetraiodofluroescein with the modification of two histidine residues per enzyme protomer. At a higher concentration (1 X 10(-5) M) a tyrosine residue is also modified. The keto substrates, ketoglutarate and oxalacetate, protect the enzyme from photoxidation. Diethylpyrocarbonate modifies three histidine residues per enzyme protomer and reduces the activity only 10%. These results suggest that the two histidine residues photoxidized through the sensitizer, are located in the active site of the enzyme, at least one of these appears to be involved in ketosubstrate binding. The other three histidines modified by diethylpyrocarbonate are likely located on the enzyme surface and are not involved in the catalytic activity of the enzyme.
来自牛肾的天冬氨酸转氨酶的全酶和脱辅基酶在2×10⁻⁶ M四碘荧光素存在下经光氧化作用80%失活，每个酶原修饰两个组氨酸残基。在较高浓度（1×10⁻⁵ M）时，一个酪氨酸残基也被修饰。酮底物α-酮戊二酸和草酰乙酸可保护该酶免受光氧化。焦碳酸二乙酯修饰每个酶原的三个组氨酸残基，仅使活性降低10%。这些结果表明，通过敏化剂光氧化的两个组氨酸残基位于酶的活性位点，其中至少一个似乎参与酮底物结合。被焦碳酸二乙酯修饰的其他三个组氨酸可能位于酶表面，不参与酶的催化活性。
