Saavedra Emma, Ramos-Casillas Laura E, Marín-Hernández Alvaro, Moreno-Sánchez Rafael, Guerra-Sánchez Guadalupe
Departamento de Bioquímica, Instituto Nacional de Cardiología, México D.F., México.
FEMS Yeast Res. 2008 Dec;8(8):1313-23. doi: 10.1111/j.1567-1364.2008.00437.x.
The kinetic parameters of the 10 glycolytic enzymes and glycolytic fluxes were determined for the first time in Ustilago maydis. Enzyme activities in yeast grown in minimal medium and harvested in the stationary stage were twofold higher than those from yeast grown in rich medium. In contrast, in yeast harvested in the exponential stage, the enzyme activities were higher in cells grown in rich medium. Phosphofructokinase activity was the lowest in the four culture conditions analyzed, suggesting that this enzyme is a flux-controlling step in U. maydis glycolysis. The V(max) and K(m) values of hexokinase and pyruvate kinase were similar under all conditions. The results revealed that U. maydis aldolase belongs to the class II type of metalo-aldolases. 3-Phosphoglycerate mutase (PGAM) activity was 2,3-bisphosphoglycerate cofactor independent, which contrasted with the cofactor dependency predicted by the amino acid sequence alignment analysis. Pyruvate was secreted by U. maydis yeast in the presence and absence of external glucose. The glycolytic enzyme activities in the U. maydis mycelial form were similar to those found in yeast, except for one order of magnitude higher phosphofructokinase and PGAM activities, thus suggesting differences in the glycolysis regulatory mechanisms between the two cellular forms.
首次测定了玉米黑粉菌中10种糖酵解酶的动力学参数和糖酵解通量。在基本培养基中生长并在稳定期收获的酵母中的酶活性比在丰富培养基中生长的酵母中的酶活性高两倍。相反，在指数期收获的酵母中，丰富培养基中生长的细胞的酶活性更高。在所分析的四种培养条件下，磷酸果糖激酶活性最低，这表明该酶是玉米黑粉菌糖酵解中的通量控制步骤。在所有条件下，己糖激酶和丙酮酸激酶的V(max)和K(m)值相似。结果表明，玉米黑粉菌醛缩酶属于II类金属醛缩酶。3-磷酸甘油酸变位酶（PGAM）的活性不依赖于2,3-二磷酸甘油酸辅因子，这与通过氨基酸序列比对分析预测的辅因子依赖性形成对比。无论有无外源葡萄糖，玉米黑粉菌酵母都会分泌丙酮酸。玉米黑粉菌菌丝体形式中的糖酵解酶活性与酵母中的相似，但磷酸果糖激酶和PGAM活性高一个数量级，因此表明两种细胞形式之间糖酵解调节机制存在差异。
