The purification and properties of the tyrosine–2-oxoglutarate transaminase of Saccharomyces cerevisiae

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Abstract
Tyrosine-2-oxoglutarate transaminase has been purified more than 100-fold with an overall yield of 33% from a dialysed crude extract of S. cerevisiae. The purified enzyme required pyridoxal phosphate for activity, and glutathione increased transaminase activity by 50%. Neither pyruvate nor oxaloacetate replaced 2-oxoglutarate and only a very slight activity was observed when tryptophan, methionine, phenylalanine, leucine or norleucine replaced tyrosine, suggesting that the enzyme is highly specific. At pH 7.8 and 37[degree] the Michaelis constants for tyrosine, 2-oxoglutarate and pyridoxal phosphate are 1.66 m[image], 2-5 m[image] and 2.38 [mu][image] respectively. The temperature coefficient over the range 27-37[degree] is 1.87 and the energy of activation determined over the range 25-46[degree] is 15.2 kg.cal. The change in heat content accompanying the formation of the enzyme-substrate complex is 6.5 kg.cal. over the temperature range 25-46[degree].