Carbohydrate Metabolism in Bakers' Yeast.^1,2 I. Time Course Study of Glucose Utilization

Abstract

The time course study of the utilization of specifically labeled glucose by yeast has been carried out under proliferating conditions. The rate of change of specific activity in the respiratory COs from the respectively labeled substrate agrees with the known breakdown pathways of glucose in this organism. Calculations were made on the basis of cumulative radiochemical recoveries of metabolic CO, from each labeled glucose which revealed that approximately 87% of the administered glucose was metabolized by way of the Embden-Meyerhof pathway in combination with the tricarboxylic acid cycle, and 13% was consumed through phosphogluconate decarboxylation. The efficiency of the utilization of each glucose carbon atom in biosynthesis also was estimated.

Identification and Estimation of Catabolic Pathways of Glucose in Fruits.

“…Acetate formed in this manner is presumably metabolized by way of the TCA process (10, 4), as also supported by the finding that the cumulative recovery of C-2 of glucose (equivalent to acetate carboxyl in the EMP-TCA scheme) in the respiratory CO2 (insert in fig 1) is considerably higher than that of C-6 of glucose (equivalent to acetate methyl) and eventually results in an overall ratio of 2 to 1 for CO2 from C-2 versus CO2 from C-6 of glucose. Similar findings have been reported in studies with proliferating yeast in which the TCA process is considered to be responsible for both respiration and biosynthesis of various carbon skeletons (9). The preferential utilization of acetate methyl carbon (hence C-6 or C-1 of glucose) in biosynthesis is thought to account for the observed ratio of C6/C2 of glucose in CO2.…”

“…The characteristic ability of the succulents to incorporate a large net amount of CO2 in the form of organic acids has been recognized for a long time (9). Although the biochemical mechanisms of this phenomenon have received a great deal of attention, the physiological role has not been fully understood.…”

PATHWAYS OF GLUCOSE CATABOLISM IN BACILLUS CEREUS

“…Using the radiorespirometric method (Wang et al, 1956), we made an estimate of the pathways GOLDMAN 1. Relation between the percentage of glucose oxidized by the hexose monophosphate pathway or the percentage of glucose-6-CI4 oxidized to C02, a measure of the terminal respiratory pathway, and the stage of development of resting Bacillus cereus terminalis suspensions.…”

The Production and Growth Characteristics of Yeast and Mycelial Forms of Candida albicans in Continuous Culture

“…The decrease in respiration quotient with increasing growth rate also implies that the catabolism of maltose and lactate to CO, is less efficient at higher than at lower growth rates. Liener & Buchanan (1951) reported that S. cerevisiae is able to satisfy up to 5 % of its carbon requirements by C 0 2 assimilation, and Wang et al (1956) proposed that up to 10 % of the pyruvate originating from glucose was involved in CO, fixation. It could well be that as the growth rate increased the importance of COz fixation reactions increased.…”