Conversion of 5'-methylthioadenosine into S-adenosylmethionine by yeast cells.

5'-Methylthio[U-14C]adenosine was used as a culture supplement for Candida utilis. The resulting S-adenosylmethionine was hydrolyzed into its structural components. Virtually none of the label of the pentose was found in the carbohydrate part of the intracellular S-adenosylmethionine. Much of it was present in the four-carbon chain of the methionine part of the sulfonium compound. The (U-14C)-labeled adenine of 5'-methylthio[U-14C]adenosine did not contribute to the labeling of the amino acid components of the sulfonium compound.

The S-n-propyl analogue of S-adenosylmethionine.

A special strain of Saccharomyces cerevisiae responded to a supplement of S-n-propyl-L-homocysteine in the culture medium by synthesizing S-adenosyl-(S-n-propyl)L-homocysteine, the S-n-propyl analogue of S-adenosylmethionine. S-n-Butyl-L-homocysteine reacted sparingly with this strain, but S-isopropyl-L-homocysteine failed to form detectable quantities of the corresponding S-adenosylsulfonium compound. The S-n-propyl compound was isolated by extraction of the cells, followed by ion-exchange chromatography, which separated it from endogenous S-adenosylmethionine. The structure was determined by hydrolytic procedures leading to overlapping fragments of known structure, 5'-n-propylthioadenosine and S-n-propyl-L-homocysteine. The new sulfonium compound was examined for its activity as n-propyl donor by substituting it for S-adenosylmethionine in methyltransferase systems. Enzymatic transpropylation was observed with S-adenosylmethionine : L-homocysteine S-methyltransferase (EC 2.1.1.10). Its rate was low in the S-adenosylmethionine : N-acetylserotonin O-methyltransferase system (EC 2.1.1.4), and below recognition with S-adenosylmethionine : guanidinoacetate methyltransferase (EC 2.1.1.2) and S-adenosylmethionine : histamine N-methyltransferase (EC 2.1.1.8).

Active transport of exogenous S-adenosylmethionine and related compounds into cells and vacuoles of Saccharomyces cerevisiae.

Saccharomyces cerevisiae 4094-B (alpha, ade-2, ura-1) in potassium phosphate buffer with glucose under aerobic conditions took up (-)S-adenosyl-l-methionine from the medium in sufficient quantity to permit the demonstration of its accumulation in the vacuole by ultraviolet micrography. The same result was obtained with (+/-)S-adenosyl-l-methionine, (+/-)S-adenosyl-d-methionine, and (-)S-adenosyl-l-ethionine. The rate of uptake was slow with (-)S-adenosyl-S(n-propyl)-l-homocysteine and S-adenosyl-d-homocysteine. S-Adenosyl-l-homocysteine was assimilated rapidly, but intracellular degradation precluded accumulation and ultraviolet micrographic studies. The uptake of 5'-methyl-, 5'-ethyl-, 5'-n-propylthioadenosine, and 5'-dimethylsulfonium adenosine was minimal.

Examination of isolated yeast cell vacuoles for active transport.

Isolated vacuoles of the yeast Candida utilis did not show active transport of S-adenosylmethionine, uric acid, and several amino acids which they concentrate in vivo.

Stability of Candida utilis cells and spheroplasts toward gravitational forces.

Candida utilis cells and spheroplasts containing uric acid crystals in their vacuoles were not damaged by the mechanical stress of centrifugation at 20,000 x g for 10 min, as judged by plating, microscopy, and spectrophotometry.