Purification and molecular properties of the (sodium + potassium)-adenosinetriphosphatase and reconstitution of coupled sodium and potassium transport in phospholipid vesicles containing purified enzyme

Modulation of cardiac glycoside inhibition of (Na+ + K+)-ATPase by membrane lipids. Difference between species

The role of lipids in the modulation of the ouabain-sensitivity of membrane (Na+ + K+)-ATPase from different species has been studied using a reconstitution procedure which promotes lipid exchange during detergent depletion by Sephadex chromatography. Hybrid reconstitution of delipidated (Na+ + K+)-ATPase preparations from bovine brain into the lipids obtained from crab nerve enzyme preparations significantly reduces the sensitivity of the brain enzyme to inhibition by ouabain. Conversely, reconstitution of crab nerve enzyme into the lipids from bovine brain enzyme preparations increases the sensitivity of the crab enzyme to ouabain inhibition. These opposing effects demonstrate the role of membrane lipids in modulating the enzyme-inhibition relationship in preparations from these different species.

Membrane asymmetry. A survey and critical appraisal of the methodology. I. Methods for assessing the asymmetric orientation and distribution of proteins

This and the companion article are aimed at surveying the methods used for the study of membrane asymmetry. The techniques employed for the assessment of the asymmetric distribution and orientation of membrane proteins are reviewed in this article, whereas those pertaining to the unequal distribution of lipids are detailed in the companion paper. The use of immunological techniques and lectins, functions of proteins and their perturbations, chemical reagents, enzymatic isotopic labeling and enzymatic cleavage of membrane proteins and physical techniques are discussed and illustrated using recent examples of their application. Whenever appropriate, problems involving crypticity and non-availability or non-reactivity of functional sites, relevant chemical functions or protein fragments to appropriate ligands, reagents or modifying enzymes are envisaged and possible modification of the exposure of proteins during preparation of ghosts and other drawbacks are discussed, the use of different techniques and control experiments in conjunction is recommended for a more realistic assessment of the distribution and orientation of proteins.

Mechanism of insulin action on resting membrane potential of frog skeletal muscle

At a concentration that stimulates the Na pump, insulin hyperpolarizes the plasma membrane of frog sartorius in the presence of substrate-free Ringer. The hyperpolarization ranged from 3.5 to 7.3 mV and averaged 4.7 mV. Ouabain, 10(-4) M, completely blocked the effect of insulin on the membrane potential. Moreover, ouabain completely reversed the insulin-induced hyperpolarization within 20 min. The hyperpolarization produced by insulin was not associated with a detectable increase in the ratio of K+ permeability to Na+ permeability nor with a detectable increase in the concentration of intracellular K+, although a depletion of K+ near the external surface of the membrane cannot be excluded. The results clearly indicate that the hyperpolarization is secondary to stimulation of the Na pump by insulin.

The role of hormones in the acclimation of fish to low temperatures

The known cases elucidating the role of hormones in the regulation of physiological and biochemical changes which occur when fish are acclimated to low temperatures are sparse, but evidence is accumulating to implicate prolactin, glucagon, insulin and perhaps thyroxine and cortisol in at least some of the physiological adjustments observed in some species. The need for further research on hormonal control mechanisms at work during low-temperature acclimation is discussed, with special emphasis placed on neuroendocrine relationships.