Participation of an intermediate of oxidative phosphorylation in ion accumulation by mitochondria

Heart mitochondria accumulate massive amounts of Mg(++) and phosphate or Ca(++) and phosphate when incubated under appropriate conditions. Studies with inhibitors of respiration, oligomycin, and uncouplers of oxidative phosphorylation indicate that the energy necessary for these reactions may be provided either in the form of ATP in the absence of electron transport, or in the form of a high-energy intermediate of oxidative phosphorylation, which operates even though ATP is not produced.

Chelation of calcium by lactose: its role in transport mechanisms

Lactose, like other sugars and polyols, prevents or delays the precipitation of calcium ion in the presence of bicarbonate buffer. That an uncharged calcium-lactose complex is formed was demonstrated by the use of paper electrophoresis and of calcium-45 as a label for the complex. Enhancement of the intestinal absorption of calcium ion by sugars could result from a complex of low molecular weight.

Cell division in a species of Erwinia. V. Effect of metabolic inhibitors on terminal division and composition of a "division" medium

Grula, E. A. (Oklahoma State University, Stillwater) and Mary M. Grula. Cell division in a species of Eriwinia. V. Effect of metabolic inhibitors on terminal division and composition of a "division" medium. J. Bacteriol. 84:492-499. 1962.-Terminal division in Erwinia spp. involves a triggering action and subsequent septum synthesis. It is a metabolic process requiring organic nitrogen and carbon and energy. The process, when triggered by pantoic acid or pantoyl lactone, is inhibited strongly by 2,4-dinitrophenol, hydroxylamine, mitomycin C, and Hg ion and to a lesser degree by cyanide, azide, 5-fluorouracil, and diisopropylfluorophosphate. Ethylenediaminetetraacetic acid completely inhibits division only when calcium ion is the triggering agent. Heating of the cells at 43 C for 10 to 20 min also completely inhibits division. Hydroxylamine, iodoacetate, and mitomycin C cause extensive lysis of growing cells. No evidence has been obtained to demonstrate the need for protein or normal ribonucleic acid synthesis in terminal division. Requirement for intact deoxyribonucleic acid (DNA) or DNA synthesis is questionable; -SH groups are not directly involved. Once triggering has occurred, septum formation appears to require synthesis of at least cell-wall mucopeptide. A "division" medium is reported and discussed.

Calcium flux in the mammalian ventricular myocardium

The exchange of Ca⁴⁵ was studied in dog myocardium by means of a newly developed perfusion technique whereby an excised papillary muscle was perfused through its own artery. This makes possible the sequential and simultaneous correlation of ionic flux with ventricular myocardial function with each muscle serving as its own control. Calcium exchange has the following characteristics: (a) The major component of calcium flux is independent of the frequency of contraction. It demonstrates a rapidly equilibrating phase (half-time, 4 to 6 minutes) and a more slowly equilibrating phase with a progressively decreasing rate constant. The flux characteristics of the more rapidly equilibrating compartment are determined by a factor or factors, in addition to simple diffusion, which increase the time required for this compartment to achieve a steady-state with respect to the vascular compartment. (b) A lesser component of exchange is stimulus-rate dependent and is characterized by an alteration in the rate of calcium turnover such that the altered influx: efflux ratio requires 20 to 25 minutes to achieve equilibrium. After this time, despite the higher stimulus rate, there is no evidence of change in total tissue calcium. (c) The initial rate of the transient response is approximately proportional to the change in stimulus rate.

Effect of azide and Ca ion on the reversible changes of protein configuration in stimulated nerves

Working with sciatic nerves from the South American frog Calyptocephalella gayi we have been able to substantiate the finding of Ungar et al., that nerve proteins undergo a reversible denaturation concomitant with a train of nerve impulses. We also showed that 0.3 mM sodium azide is capable of impairing the reversibility of those changes. Furthermore, 10 meq/liter of calcium ion applied to extracts of resting nerves induce configurational rearrangements in the proteins similar to those produced during stimulation. We also proved that nerves previously kept in low calcium Ringer's solution do not show configurational changes upon stimulation. A tentative interpretation of the results described is that the configurational changes are a consequence of the extra influx of calcium ion due to nerve impulse propagation.

THE ADENOSINE-TRIPHOSPHATASE ACTIVITY OF ADRENAL CHROMAFFIN GRANULES

1. The preparation of a fraction containing highly purified chromaffin granules from the bovine adrenal medulla is described. 2. The fraction contains an adenosine-triphosphatase activity that is stimulated by Mg(2+) and that cannot be explained by contamination with mitochondria or microsomes. 3. It is suggested that the adenosine-triphosphatase activity is related to the uptake of cate-cholamines by the chromaffin granules.

PURIFICATION AND PROPERTIES OF STAPHYLOCOCCAL BETA-HEMOLYSIN. I. PRODUCTION OF BETA-HEMOLYSIN

Haque, Riaz-ul (Ohio State University, Columbus), and Jack N. Baldwin. Purification and properties of staphylococcal beta-hemolysin. I. Production of beta-hemolysin. J. Bacteriol. 88:1304-1309. 1964.-Highest activity of beta-hemolysin was observed when buffered saline (pH 7.0) containing 0.001 m magnesium sulfate was used as a diluent, and the tubes were incubated at 37 C for 80 min and then refrigerated for 30 min. Either Heart Infusion semisolid agar or a dialysate of Heart Infusion containing 0.3% agar was suitable for the production of large quantities of beta-hemolysin. The concentration of beta-hemolysin in semisolid and broth cultures was greatest after incubation for 24 hr. Continued incubation resulted in a loss of active hemolysin in broth cultures but not in semisolid agar cultures. Incubation in atmospheres containing 20% carbon dioxide greatly enhanced the production of beta-hemolysin. The presence of fermentable sugars inhibited the production of beta-hemolysin. Highest yields of beta-hemolysin were obtained when the initial pH of the medium was 5.5 to 5.8.

HEART ACTION POTENTIAL: DEPENDENCE ON EXTERNAL CALCIUM AND SODIUM IONS

The height of the overshoot of the action potential recorded from frog ventricles is markedly less sensitive to lowering the external sodium concentration than predicted by the sodium-hypothesis of excitation, and it is surprisingly sensitive to changes in the external calcium concentration. These observations are explained by a mechanism in which there is competition between sodium and calcium ions, in the excitable membrane, for anionic sites which control the inward current of sodium ions at the crest of the action potential.