Degradation of aromatic amino acids inCandida maltosa

Enhanced excretion of intermediates of aromatic amino acid catabolism during chlorophenol degradation due to nutrient limitation in the yeast Candida maltosa

Incubation of phenol-induced cells of the yeast Candida maltosa SBUG 700 with mono- and dichlorophenols resulted in the formation of metabolites of the substrates and of further metabolites not related to the degradation pathway of the substrates. These additional compounds, identified as 4-hydroxyphenylacetic acid (4-HPA), phenylacetic acid (PA), indolylacetic acid (IA) and indolylethanol (i.e.) by means of HPLC and GC/MS, were not excreted in incubation experiments with glucose. The excretion of these metabolites of aromatic amino acid metabolism is not caused by toxic effects of the phenol derivatives, but seems to be a result of carbon and nitrogen starvation of yeast cells.

Neisseria gonorrhoeae possesses two nicotinamide adenine dinucleotide-independent lactate dehydrogenases

An important metabolic capability of Neisseria gonorrhoeae is the utilization of host-derived lactate. Two isoenzymes of the membrane-associated, pyridine dinucleotide-independent type of lactate dehydrogenase (iLDH) participate in lactate assimilation, but exhibit distinctive properties. Isoenzyme iLDH-I utilized lactate exclusively as substrate, exhibiting a preference for the D-isomer. In contrast, isoenzyme iLDH-II exhibited broad substrate specificity (lactate, phenyllactate, and 4-hydroxyphenyllactate), but was stereospecific for the L-isomers. These results explain the difficulty in isolating mutants unable to utilize lactate.

In vitro tryptophan catabolism by Leishmania donovani donovani promastigotes

Metabolism of tryptophan by promastigotes of Leishmania donovani donovani was investigated in cells suspended in a simple buffer solution supplemented with glucose. Metabolites from supernatant and lysed cell pellets were analyzed by capillary gas liquid chromatography and 13C nuclear magnetic resonance spectroscopy, with structural confirmation by gas liquid chromatography-mass spectrometry. Tryptophan does not appear to serve as a carbon energy source for L. d. donovani promastigotes since parasites could survive for only short periods in buffer containing tryptophan without glucose, levels of tricarboxylic acid cycle intermediates remained unchanged in the presence of added tryptophan and label from [13C]tryptophan was not detected in any of the intermediates. Leishmania d. donovani catabolized L-tryptophan via aminotransferase and aromatic lactate dehydrogenase reactions to form one major end product, indole-3-lactic acid. The activity of aromatic lactate dehydrogenase required manganese and was NADH-dependent in these organisms that lack lactate dehydrogenase. Promastigotes taken from the mid-log stage of growth produced higher concentrations of indole-3-lactic acid than those from the stationary stage. Conservation of a similar tryptophan catabolic pathway among four Leishmania species suggests the pathway is physiologically important to the parasites themselves.

Occurrence of the general control of amino acid biosynthesis in yeasts

The response of three amino acid biosynthetic enzymes, threonine dehydratase, tyrosine aminotransferase and saccharopine dehydrogenase, to conditions of histidine, tryptophan or lysine limitation was investigated in 15 yeast species. The activities of all these enzymes increased about two- to fourfold as a result of action of the general control of amino acid biosynthesis in Brettanomyces anomalus, Candida maltosa, Hansenula polymorpha, Rhodosporidium toruloides, Saccharomyces cerevisiae and Yarrowia lipolytica. No evidence for the existence of the general control was found in Candida brumptii, Candida utilis, Hansenula anomala, Hansenula henricii, Kluyveromyces marxianus, Pichia guilliermondii, Saccharomycopsis capsularis, Trichosporon adeninovorans and Trigonopsis variabilis.