Kakebeeke P I, de Wit R J, Konijn T M
J Bacteriol. 1980 Jul;143(1):307-12. doi: 10.1128/jb.143.1.307-312.1980.
Folic acid attracts vegetative amoebae of Dictyostelium discoideum. Secreted by bacteria, it may act as a food-seeking device. The inactivation of this attractant is catalyzed by a deaminase. As assay has been developed to measure the folic acid deaminase activity. In addition to cell-surface an intracellular deaminase, the amoebae of D. discoideum release the enzyme into the medium. The pH optimum of the extracellular enzyme was 6.0, and higher for the cell-associated deaminases. The extracellular enzyme was secreted maximally by vegetative amoebae, and its activity diminished during cell differentiation. The cell-surface bound enzyme was less active than the extracellular enzyme, and its activity decreased twofold during a 6-h starvation period. The enzyme activity of homogenates and 48,000 x g pellets diminished during this period 35 to 40%. The supernatant of a homogenate had a higher deaminase activity than the homogenate itself or its pellet; this suggests the presence of an inhibitor in the particulate fraction. The underlying mechanism for inactivation of folic acid has similar characteristics as that for inactivation of cyclic adenosine monophosphate.
叶酸能吸引盘基网柄菌的营养性变形虫。它由细菌分泌，可能起到寻找食物的作用。这种引诱剂的失活由一种脱氨酶催化。已开发出一种测定叶酸脱氨酶活性的方法。除了细胞表面和细胞内的脱氨酶外，盘基网柄菌的变形虫还会将该酶释放到培养基中。细胞外酶的最适pH为6.0，而与细胞相关的脱氨酶的最适pH更高。细胞外酶由营养性变形虫最大量地分泌，其活性在细胞分化过程中降低。细胞表面结合的酶比细胞外酶活性低，并且在6小时饥饿期内其活性降低两倍。在此期间，匀浆和48,000×g沉淀的酶活性降低35%至40%。匀浆的上清液比匀浆本身或其沉淀浆沉淀具有更高的脱氨酶活性；这表明颗粒部分存在抑制剂。叶酸失活的潜在机制与环磷酸腺苷失活的机制具有相似的特征。
