James B. Evans

A study of the methylene blue and oxygen inhibition of pyruvate oxidation by Micrococcus pyogenes var. aureus

Abstract The oxidation of pyruvate by resting-cell suspensions of a coagulasepositive, enterotoxin-producing strain of Staphylococcus aureus has been studied. With moderate substrate levels (10–20 μM per Warburg cup) pyruvate was oxidized almost exclusively to acetate, carbon dioxide, and water. The respiratory quotient of this oxidation varied from 1.4 to 1.9 depending on the cell preparation used. The results indicate that some of the substrate was oxidized beyond the acetate level (R.Q., 2.0). Methylene blue or oxygen exerted an inhibitory effect upon pyruvate oxidation, and, under certain conditions, thiamine and magnesium overcame this inhibition. Evidence is presented to support the hypothesis that this organism possesses two separate systems for pyruvate oxidation. Washed-cell suspensions oxidize pyruvate predominantly by a system that is sensitive to methylene blue and oxygen. When this system is inhibited the competing system becomes dominant. However, the washed cells are deficient in thiamine and magnesium for optimum functioning of this latter system. A by-product of this second system is acetoin, indicating that there is an intermediate compound that may be either oxidized to acetate or condensed to form acetoin. If the washed cells are provided with a high substrate level or are supplemented with additional thiamine and magnesium, some of the pyruvate is metabolized by the second pathway even in the absence of an inhibitor for the first system.

Uptake and transamination of amino acids by Streptococcus faecium

Abstract A technique, which by first depleting the cellular freely extractable amino acids of Streptococcus faecium rendered subsequent amino acid uptake readily demonstrable, was used to prepare cell suspensions with which the uptake of seven amino acid species was studied. All the amino acids studied, except arginine, required glucose for uptake (including lysine, contrary to previous reports). D -Amino acids were taken up with the same facility as their L -isomers. Uptake of exogenous amino acids was accompanied by (a) extensive transamination of the amino acid taken up, if it was a type not characteristically found in cell walls of this genus and (b) appearance of cellular freely extractable alanine, lysine, and glutamic and aspatic acids from a cellular component, whether or not they had been added to the suspension. The latter observation supports a previous postulate that S. faecium contains a heat-stable amino acid reservoir, noted in the present study to be connected to its amino acid transport system. Considered together, these observations suggest how transaination and the reservoir (or cell-wall components), without necessarily being part of the amino acid transport system, may be used by S. faecium to circumvent the thermodynamic limitation placed upon concentrative amino acid accumulation by the concentration gradient between these compounds within and without the cell: the cell, in effect, stores amino acids taken up both as their freely extractable ketonic precursors, readily regenerating the amino acid by transamination, and in reversible combination with the reservoir (or cell-wall components).