14C] Glucose metabolism in fungal cells.

Abstract

SUMMARY: The incorporation pattern of 14C from [14C]glucose by the fungus Zygorhynchus moelleri has been investigated. The following substances became labelled in incubation periods of 6 sec. to 30 min.: the monophosphates of glucose, fructose, sedoheptulose, ribose, maltose, glycerol, gluconic acid, glyceric acid, enolpyruvic acid and guanosine; the diphosphates of fructose, glucose, glyceric acid, adenosine, uridine, inosine and guanosine; the triphosphates of adenosine and uridine; uridinediphosphoglucose and uridinediphosphoribose; free maltose and fructose; aspartic acid, glutamic acid, alanine, valine, tyrosine, proline, histidine, threonine, citrulline and glutamine; malic acid, citric acid, succinic acid, fumaric acid and glyceric acid. A small percentage of the 14C was present in unidentified substances. The kinetics of the incorporation of 14C, first into uridinediphosphoglucose, then into maltose phosphate, and finally into free maltose, suggests this sequence of compounds for the biosynthetic pathway of maltose formation. The main effects of starvation of the cells by shaking them in phosphate buffer for 24 hr. were an increased % incorporation of 14C into maltose and the sugar phosphates, and a decreased % incorporation into amino acids, organic acids and nucleotides. The addition of a small amount of ammonia to starved cells increased the absolute rate of incorporation of 14C from labelled glucose into soluble cellular constituents; however, while the % of the total soluble 14C found in the nucleotides was markedly increased when ammonia was added, the % in the sugar phosphates decreased. In the presence of azide, the incorporation of 14C by starved cells into maltose and the nucleotides was severely inhibited and the incorporation into amino acids was somewhat increased. Thus, one of the most important results of starvation was to prevent incorporation of 14C into the nucleotides, organic acids and amino acids, while the addition of ammonia overcame the effects of starvation and promoted nucleotide synthesis. Ammonia had very little effect on the cells in the presence of azide. A kinetic study of the sequence in which 14C was detected in these compounds indicated that glucose was metabolized by both the glycolysis and the oxidative pathways, and later by the tricarboxylic acid cycle.