Yvon M, Thirouin S, Rijnen L, Fromentier D, Gripon J C
Unité de Recherche de Biochimie et Structure des Protéines, I.N.R.A., Jouy-en-Josas, France.
Appl Environ Microbiol. 1997 Feb;63(2):414-9. doi: 10.1128/aem.63.2.414-419.1997.
The enzymatic degradation of amino acids in cheese is believed to generate aroma compounds and therefore to be involved in the complex process of cheese flavor development. In lactococci, transamination is the first step in the degradation of aromatic and branched-chain amino acids which are precursors of aroma compounds. Here, the major aromatic amino acid aminotransferase of a Lactococcus lactis subsp. cremoris strain was purified and characterized. The enzyme transaminates the aromatic amino acids, leucine, and methionine. It uses the ketoacids corresponding to these amino acids and alpha-ketoglutarate as amino group acceptors. In contrast to most bacterial aromatic aminotransferases, it does not act on aspartate and does not use oxaloacetate as second substrate. It is essential for the transformation of aromatic amino acids to flavor compounds. It is a pyridoxal 5'-phosphate-dependent enzyme and is composed of two identical subunits of 43.5 kDa. The activity of the enzyme is optimal between pH 6.5 and 8 and between 35 and 45 degrees C, but it is still active under cheese-ripening conditions.
奶酪中氨基酸的酶促降解被认为会产生香气化合物，因此参与了奶酪风味形成的复杂过程。在乳酸球菌中，转氨作用是芳香族和支链氨基酸降解的第一步，而这些氨基酸是香气化合物的前体。在此，对一株乳酸乳球菌乳脂亚种的主要芳香族氨基酸转氨酶进行了纯化和表征。该酶能催化芳香族氨基酸、亮氨酸和蛋氨酸的转氨反应。它以与这些氨基酸对应的酮酸和α-酮戊二酸作为氨基受体。与大多数细菌芳香族转氨酶不同的是，它不作用于天冬氨酸，也不使用草酰乙酸作为第二底物。它对于芳香族氨基酸转化为风味化合物至关重要。它是一种依赖磷酸吡哆醛的酶，由两个相同的43.5 kDa亚基组成。该酶的活性在pH 6.5至8以及35至45摄氏度之间最佳，但在奶酪成熟条件下仍具有活性。
