Regulation of ATP hydrolysis in hepatoma 22a mitochondria.

A decrease in the rate of ATP hydrolysis was observed after preincubation of intact mitochondria from hepatoma 22a with an uncoupler. This effect is due both to a decrease in the rate of ATP transport and to an inactivation of the F0F1-ATPase. The former effect is shown to result from an uncoupler-induced ADP efflux.

Activation of a complex of ATPase with the natural protein inhibitor in submitochondrial particles.

Almost all ATPase molecules in submitochondrial particles, isolated from beef heart mitochondria in the presence of MgATP, are in an active complex with the natural protein inhibitor (IF1). In de-energized particles at high ionic strength a slow and irreversible ATPase activation is found to occur due to a dissociation of the enzyme-inhibitor complex. The pH-dependence of this process points out that deprotonation of IF1 molecule is an essential step in the dissociation of the complex.

[Various indicators of brain metabolism during hypoxia and hyperthermia].

Hypoxic, thermal and radiation tolerance of rats exposed to hypoxia and overheating for 4 to 22 days was measured. Activities of succinic dehydrogenase, lactate dehydrogenase and alkaline phosphomonoesterase as well as water content in the brain were examined biochemically and histochemically. Brain tolerance and metabolism varied in a phasic manner.

The interaction of MgADP with H+ -ATPase in rat liver mitochondria.

The activating anions are found to induce an unexpectedly high (up to 8-fold for sulphite) increase of ATPase activity in intact rat liver mitochondria. This effect is not determined by the observed changes in Km and Ki (ADP) values. The stimulation seems to be caused by dissociation of the inactive complex of ATPase with Mg.

The effect of the natural protein inhibitor on H+-ATPase hepatoma 22a mitochondria.

The uncoupler-induced inactivation of H+-ATPase in hepatoma 22a and mouse liver mitochondria has been studied. The dependence of this process on delta microH, and pH and ATP was established. The inactivated ATPase could be reactivated at alkaline pH values in the absence of ATP.

The effect of phospholipids on the activity of mitochondrial pyrophosphatases. Lipidized soluble mitochondrial pyrophosphatase: the coupling factor for oxidation and phosphorylation.

The effect of temperature on the hydrolase activity of mitochondrial pyrophosphatases, i.e. soluble (PPase I) and membrane (PPase II), has been studied.

[The role of lipids in the regulation of ATP and PPi synthesis in mitochondria].

It was demonstrated previously that mitochondria of higher and lower eukaryotes can synthesize, in the course of oxidative phosphorylation, not only ATP but also inorganic pyrophosphate (PPi). Two PPases were isolated from bovine heart mitochondria (soluble--PPase I and membrane--PPase II). Coupling PPase II, in contrast to PPase I, contains phosphatidyl choline, but PPase I is lipidized readily in the presence of different phospholipids.

[Effects of lipids on the activity of soluble mitochondrial pyrophosphatase and its conversion to the membrane-bound form].

The effects of lipids on the activity of soluble and membrane-bound pyrophosphatase from beef heart mitochondria were studied. An addition of total mitochondrial lipid, phosphatidyl choline, phosphatidyl ethanolamine or cardiolipin resulted in stimulation of the enzymatic activity and an increase in thermal stability of the soluble enzyme. The maximal activating effect was exerted by the total mitochondrial lipid and phosphatidyl choline.