Carbohydrate Metabolism

Abstract

INTRODUCTION
Scope and Organization
This paper, which I dedicate to B. L. Horecker, is a review of intermediary carbohydrate metabolism in Saccharomyces. It emphasizes the central pathways, including glycolysis and the tricarboxylic-acid (TCA) cycle, and also treats some specific catabolic routes; biosynthetic pathways are not included. It covers some of the same material as the review by Sols et al. (1971), in addition to mutant studies.

Many of the reactions with their gene symbols (some already used, others suggested here) are shown in Figure 1 and are also listed in Table 1 with references to structural and genetic studies. The gene symbols are not intended as abbreviations for the enzymes and appear in the text mainly for convenience in referring to Figure 1 and Table 1.

An Overall View of Yeast Metabolism
Strains of Saccharomyces in common use for genetics and biochemistry grow best by fermentation, even aerobically; this is illustrated in Table 2. Data from Lagunas (1976) show aerobic growth in batch culture. It was fastest on glucose (k, the first-order growth rate constant, of 0.34 hr⁻¹), but it was inefficient, with only 13% assimilation to cell material and most of the remaining carbon accumulating as fermentation products. Batch aerobic growth on galactose was a little slower than on glucose (k of 0.26) and there was 26% assimilation, but fermentation products still accounted for 55% of the sugar used. In contrast, aerobic growth on ethanol was slow (k of 0.087) but efficient (39% assimilation).

The accumulation of fermentation products...