Glucose, aerobic oxidation yeast

Filipin inhibited anaerobic and aerobic oxidation of glucose by S. cerevisiae but had no effect on the oxidative capacity of cell-free homogenates [141]. The antibiotic reduced the dry weight of the yeast with the loss of nitrogen and phosphorus from the cell. This was the first indication that the observed effects of polyenes on fungal metabolism were a consequence of altered cellular permeability and the fungicidal effect was the result of the loss of vital cytoplasmic components. 

When grown under aerobic conditions, the yeast produces two ATP molecules from one molecule of glucose by substrate-level phosphorylation in glycolysis. The two molecules of pyruvate produced can then be completely oxidized to CO2, and each yields a further 15 molecules of ATP. This leads to a slow decrease in the concentration of glucose, a steady production of CO2, and relatively little change in the amount of ATP. Also, the two molecules of NADH can be reoxidized to NAD+ by the electron-transport system. (This produces yet more ATP, as discussed in Chap. 14.)... 

Rates of Oxidative Respiration and Non-Oxidative Fermentation by Yeasts Growing Aerobically in 3% D-Glucose"... 

FIGURE 17.1 One molecule of glucose is converted to two molecules of pyruvate. Under aerobic conditions, pyruvate is oxidized to COj and H2O by the citric acid cycle (Chapter 19) and oxidative phosphorylation (Chapter 20). Under anaerobic conditions, lactate is produced, especially in muscle. Alcoholic fermentation occurs in yeast. The NADH produced in the conversion of glucose to pyruvate is reoxidized to NAD+ in the subsequent reactions of pyruvate. 

Under aerobic conditions and in the absence of high concentrations of glucose, yeast respires glucose. Under these circumstances pyruvic acid is oxidized and decarboxylated by the so-called pyruvate dehydrogenase complex. This system comprises three separate enzyme activities and is located within mitochondria. The three separate enzymes are pyruvate dehydrogenase, dihydrolipoyl transacetylase and dihydrolipoyl dehydrogenase (A, B and C in... 

Fermentation a form of metabolism producing incompletely oxidized end products. Per unit of substrate, F. yields far less energy than respiration, e.g. a yeast cell obtains 2 molecules ATP per molecule of glucose when it ferments glucose to ethanol, whereas complete respiration would yield 38 molecules of ATP (see Alcoholic fermentation). Strictly speaking, F. is an anaerobic process (Pasteur defined F. as life without air ) but the term is also widely and loosely applied to certain aerobic processes, such as acetic acid F., and to any industrial production process employing microorganisms in a fermentor (see Fermentation techniques). 

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