Doctor V M, Oró J
Biochem J. 1969 May;112(5):691-7. doi: 10.1042/bj1120691.
Non-enzymic transamination reactions at 85 degrees between various amino acids and alpha-oxoglutaric acid are catalysed by metal ions, e.g. Al(3+), Fe(2+), Cu(2+) and Fe(3+). The reaction is optimum at pH4.0. Of the 14 amino acids studied histidine is the most active. In the presence of Al(3+) histidine transaminates with alpha-oxoglutaric acid, forming glutamic acid and Al(3+)-imidazolylpyruvic acid complex as the end products. However, in the presence of Fe(2+) or Cu(2+) the products are glutamic acid and a 1:2 metal ion-imidazolylpyruvic acid chelate. The greater effectiveness of histidine in these reactions is attributed to the presence of the tertiary imidazole nitrogen atom, which is involved in the formation of stable sparingly soluble metal ion-imidazolylpyruvic acid complexes or chelates as end products of these reactions. Of the metal ions studied only Al(3+), Fe(2+), Fe(3+) and Cu(2+) are effective catalysts for the transamination reactions, and EDTA addition completely inhibits the catalytic effect of the Al(3+). Spectrophotometric evidence is presented to demonstrate the presence of metal ion complexes of Schiff bases of histidine as intermediates in the transamination reactions. These results may contribute to understanding the role of histidine in enzyme catalysis.
在85摄氏度下，各种氨基酸与α-酮戊二酸之间的非酶转氨反应由金属离子催化，例如Al(3+)、Fe(2+)、Cu(2+)和Fe(3+)。该反应在pH4.0时最适宜。在所研究的14种氨基酸中，组氨酸活性最高。在Al(3+)存在下，组氨酸与α-酮戊二酸发生转氨反应，最终生成谷氨酸和Al(3+)-咪唑基丙酮酸络合物。然而，在Fe(2+)或Cu(2+)存在下，产物是谷氨酸和1:2的金属离子-咪唑基丙酮酸螯合物。组氨酸在这些反应中更有效是由于叔咪唑氮原子的存在，它参与形成稳定的微溶性金属离子-咪唑基丙酮酸络合物或螯合物，作为这些反应的终产物。在所研究的金属离子中，只有Al(3+)、Fe(2+)、Fe(3+)和Cu(2+)是转氨反应的有效催化剂，添加EDTA会完全抑制Al(3+)的催化作用。通过分光光度法证明了在转氨反应中存在组氨酸席夫碱的金属离子络合物作为中间体。这些结果可能有助于理解组氨酸在酶催化中的作用。
