Multiplicity of the amino acid permeases in Saccharomyces cerevisiae. IV. Evidence for a general amino acid permease

Kinetic and genetic evidences are presented to show that, in addition to specific amino acid permeases, Saccharomyces cerevisiae has a general amino acid permease which catalyzes the transport of basic and neutral amino acids, but most probably not that of proline. The general amino acid permease appears to be constitutive, and its activity is inhibited when ammonium ions are added to the culture medium. A mutant which has lost the general amino acid permease activity was isolated. Its mutation, named gap (general amino acid permease), is not allelic to the aap (amino acid permease) mutation of Surdin et al., which has a quite different phenotype and cannot be considered as having selectively lost the general amino acid permease activity.

Oxidative phosphorylation in Escherichia coli

A particulate fraction obtained from sonic extracts of Escherichia coli was able to carry out oxidative phosphorylation with NADH2 as substrate and to perform the energy-dependent transhydrogenase reaction. The latter activity was more stable, suggesting that different coupling factors were involved in both systems. A coupling-factor preparation stimulated both reactions but to differing degrees. Oxidative phosphorylation was more sensitive than the transhydrogenase to irradiation with ultraviolet light, which destroyed a site located between flavin and cytochrome b1 in the respiratory chain. Experiments with dicumarol and pentachlorophenol suggested that these inhibitors and the coupling-factor preparation also interacted with the electron-transport chain at this site. Further evidence for the existence of two sites of energy coupling was obtained by the selective inhibition of the transhydrogenase by carbonyl cyanide m-chlorophenylhydrazone, EDTA, triiodothyronine, 2,4-dinitrophenol, and hydroxylamine. The effects of calcium and of phosphate ions were consistent with the involvement of non-phosphorylated high-energy intermediates in oxidative phosphorylation and the energy-dependent transhydrogenase.

Reduced nicotinamide-adenine dinucleotide oxidation in Escherichia coli particles. 3. Cellular location of menadione reductase and ATPase activities

Sonic extracts of Escherichia coli were fractionated to membrane-wall, small-particle, and soluble fractions. Menadione reductase and ATPase activities were found in all fractions. The menadione reductase activity of the soluble fraction was resolved into three enzymes. Enzymes with properties similar to two of these could be released from the particulate fraction by treatment with sodium dodecyl sulfate or chelating agents. The major ATPase of the particulate fractions was solubilized by detergent. Osmotic shock experiments suggested that it was located outside the plasma membrane in the intact cell. It differed from the ATPase of the soluble fraction. An enzyme resembling the latter ATPase was solubilized from the small-particle fraction by chelating agents and could be rebound in the presence of magnesium ions. Solubilized menadione reductase was not rebound to particulate fractions under these conditions.