Activities and properties of the ammonium assimilation enzymes NADP+-dependent glutamate dehydrogenase (GDH), glutamate synthase (GOGAT) and glutamine synthetase (GS) were determined in batch and continuous cultures of Candida albicans. NADP+-dependent GDH activity showed allosteric kinetics, with an So.s for 2-oxoglutarate of 7.5 mM and an apparent K , for ammonium of 5-0 mM. GOGAT activity was affected by the buffer used for extraction and assay, but in phosphate buffer, kinetics were hyperbolic, yielding K , values for glutamine of 750 p~ and for 2-oxoglutarate of 65 p~. The enzymes GOGAT and NADP+-dependent GDH were also assayed in batch cultures of Saccharomyces cerevisiae and three other pathogenic Candida spp. : Candida tropicalis, Candida pseudotropicalis and Candida parapsilosis. Evidence is presented that GSlGOGAT is a major pathway for ammonium assimilation in Candida albicans and that this pathway is also significant in other Candida species.

Since cyclamates were first introduced in the early 1950s, arguments have raged over the potential carcinogenicity of this artificial sweetener. Concern over the safety of cyclamates arises from observations that some individuals and experimental animals can metabolize cyclamate to cyclohexylamine and that cyclohexylamine has been shown to produce testicular atrophy in experimental animals. This study examines the absorption, excretion, and metabolism of cyclamate, particularly its conversion to cyclohexylamine. In addition, the potential toxicity and pharmacology of cyclohexylamine are discussed. Diabetes Care 12:50-55, 1989