Morphology and ATP-ase of isolated mitochondria

Changes in the morphology of rat liver mitochondria brought about by different methods of isolation and the concomitant changes in ATP-ase activity were studied. The morphology was investigated with the electron microscope. It was found that the ATP-ase activity of the isolated mitochondria cannot be readily correlated with the morphology of the mitochondria. The ATP-ase found in these preparations was latent, resembling the enzyme described in mitochondria prepared in 0.25 M sucrose. In confirmation of earlier results the use of 0.88 M sucrose yielded preparations with a higher initial ATP-ase than did other methods. Preparation in 0.25 M sucrose resulted in round, swollen mitochondria of which 30 to 40 per cent appeared to have lost a substantial part of the mitochondrial matrix. Preparations in 0.44 to 0.88 M sucrose contained mainly rod-shaped mitochondria plus a small amount of another type of swollen mitochondria. The matrix of mitochondria isolated in 0.88 M sucrose was highly condensed. By the use of 0.44 M sucrose adjusted to pH 6.2 with citric acid, it was possible to isolate, for the first time, mitochondria closely resembling those in situ and containing latent ATP-ase.     

Effect of vasopressin on the ATP-ase activity of microsomal fractions of rabbit heart and liver]

It was shown that intravenous injection of vasopressin in a dose of 5 pressor units per 1 kg of body weight led to changes in the ATP-ase activity of the heart and liver microsomes in one hour. These changes coursed in a different direction, i.e. ATP-ase activity of the heart microsomes increased, and ATP-ase activity of the liver microsomes decreased.     

Electron-microscopic histochemical study of myosin ATP-ase activity

Summary The sites of calcium-activated myosin ATP-ase reaction have been determined by a method modified from that of Padykula and Hermann. On coherent muscle preparations the enzyme was found to be mainly active in the segment A, although reaction was sometimes observed in the strip Z also. In several cases the precipitate appeared in a spherical shape in the segment A. Since no such phenomenon was observed in isolated bundles of myofibrils it is supposed to be an artefact. The reaction appeared in fibre bundles at 300 to 400 Å intervals, and a certain spatial periodicity was observed also on isolated thick filaments.     

Spontaneous activity of the isolated rabbit superior cervical sympathetic ganglion

Investigation of spontaneous activity (mean amplitude of spikes 200–300 µV, frequency from 0.07 to 2.9 Hz) in the rabbit superior cervical sympathetic ganglion by the sucrose gap method showed that this activity was completely blocked by D-tubocurarine and hexamethonium; its frequency was increased in hypertonic solution, by an increase in the external potassium concentration, and by the addition of theophylline and ethanol. These observations suggest that the activity observed is due to spontaneous liberation of acetylcholine mediator from preganglionic nerve endings. However, addition of tetrodotoxin and an increase in the external calcium concentration to 10 mM block spontaneous activity in the ganglion. This suggests that the observed spontaneous activity consists of action potentials.     

Electron-cytochemical study of ATP-ase activity in the brain after death]

The lead method was applied to determine the localization of the ATP-asic activity in the rat and human brains at different periods after death. This activity was revealed in the cytoplasm of the cells, chromatin and the nucleolus, and also in the synaptic terminals. In the vascular capillaries the product of reaction was localized in the basal layer and on the cytomembrane of the endothelial cells. The results obtained pointed to a good preservation of the ATP-asic activity in the postmortem brain.     

Evidence for ATP-ase activity of arrestin from bovine photoreceptors.

In vertebrate photoreceptors the soluble protein arrestin (45 kDa) is involved in controlling the light dependent activity of receptor proteins such as transducin or the cGMP-phosphodiesterase. Arrestin has further been identified as the retinal-S-antigen which is assumed to cause the autoimmune disease uveitis. In a first communication a binding of the nucleotide ATP to arrestin was described. In this subsequent study it is shown that arrestin is also able to hydrolyse ATP at a rate of (5.1 +/- 0.3) x 10(-3) U/mg.min with C1/2 = 93 +/- 5 nM and a Hill coefficient n = 1.8 +/- 0.1 at pH 7.2 and 20 degrees C. These findings suggest a new insight into the process of regulating photoreceptor activity.