Stimulation of phosphoenolpyruvate formation by oleic acid and other uncouplers of oxidative phosphorylation in rabbit liver mitochondria

Morphology and physiology of the dimorphic fungus Mucor circinelloides (syn. M. racemosus) during anaerobic growth

The dimorphic Mucor circinelloides requires an anaerobic atmosphere and the presence of 30% CO2 to grow as a multipolar budding yeast, otherwise hyphal growth predominates. Establishing other means to control the morphology would be a distinct advantage in the development of a fermentation process for this organism for the production of heterologous proteins. Thus, conditions suppressing polarised growth while at the same time abolishing the CO2 requirement were investigated in submerged cultivations. It was found that supplementing cultures with mixtures of ergosterol and Tween 80 resulted in yeast-like growth under 100% N2. Their impact on growth and morphological development was assessed at a range of concentrations. Maximum biomass levels and the specific growth rate decreased at elevated levels of ergosterol and Tween 80. Possible effects of carbon dioxide and the added fatty acid/sterol mixture on supporting yeast growth by influencing the fluidity of the plasma membrane or affecting polarised growth are discussed.

The compartmentation of nucleoside diphosphate kinase in mitochondria

The compartmentation of nucleoside diphosphate kinase (NDPK) was studied in mitochondria isolated from heart and liver of rat, rabbit, and pigeon. Compartmentation was assessed by determining latencies of enzyme activities, fractionating mitochondria with digitonin, and treating mitochondria with trypsin in the presence and absence of digitonin. NDPK activity in pigeon liver mitochondria was five- and seven-fold higher than in rat and rabbit liver mitochondria. The ratios of NDPK activities in liver vs. heart mitochondria were about 15 for rat, 2 for rabbit, and more than 40 for pigeon. Nearly all NDPK in pigeon liver mitochondria is in the matrix space, but outside the matrix in rat and rabbit liver mitochondria. Most NDPK in pigeon heart mitochondria was located outside the matrix while a significant fraction may be in the matrix of rat and rabbit heart mitochondria. These results are discussed relative to the assumed role that mitochondrial NDPK transfers the phosphoryl group of GTP produced in the Krebs cycle to the adenine nucleotide pool.

The effect of inhibitors on the formation of phosphoenolpyruvate by rat liver mitochondria

1. Rat liver mitochondria oxidizing malate produce PEP (phosphoenolpyruvate) without the addition of ATP or other nucleotides. 2. The addition of oligomycin in the presence of 2,4-dinitrophenol did not abolish PEP formation and in some instances stimulated its formation. 3. Formation of PEP was inhibited by arsenate. 4. Arsenite decreased PEP formation and caused accumulation of pyruvate. 5. Added GTP and ITP had no effect on PEP formation. 6. PEP formed from malate in the presence of GTP and labelled P(i) had a specific radioactivity approximately the same as the P(i) with no contribution from the phosphate of the added GTP. 7. There was no parallelism between the effects of inhibitors on PEP formation from malate and their effects on the assayed activity of PEP carboxykinase. 8. In a direct comparison it was shown that the PEP carboxykinase content of mitochondria was insufficient to account for the PEP formation from malate. 9. Consideration of the kinetic characteristics of PEP carboxykinase and mitochondrial content of oxaloacetate and GTP show that this enzyme cannot account for the PEP formed from malate by mitochondria.