3. Adenylyl(fl,y-methylene)diphosphonate (AMP-PCP) and AMP had no restituting effect, indicating that in order to act ATP must be hydrolysed.4. Na+-dependent Mg2+ outflow is not inhibited by vanadate concentrations that completely block the Ca2+ or Na+ pump. Therefore, the Nao-Mgi exchange does not fall into the class of cation pumps of the E1E2 type.5. Yet the fact that reversal of the Na+ gradient fails to reverse the direction of the Na+-dependent Mg2+ transport in human red cells (Lildi & Schatzmann, 1987) and that at equal Na+ concentration inside and outside the rate of Mg2+ transport is still 50 % of that at a Na+ concentration difference of -100 mm across the membrane suggests that the Na+ gradient, or the cation gradients in general, are not the only driving forces for Mg2+ movement. The assumption that there is energy input from ATP hydrolysis is compatible with these observations, whereas proposing the action of a protein kinase fails to explain them.6. It is concluded that the Na+-Mg + exchange system has an absolute requirement for ATP and that it is more probable that ATP is supplying energy for transport rather than activating transport by protein phosphorylation or simply by binding.

Purified human erythrocyte membrane acetylcholinesterase was incorporated into vesicles of various lipid compositions. The activities of the free and the lipid-associated enzyme were assayed at temperatures between 4 'C and 40 'C and the results were visualized as plots of log z' versus 1/T (Arrhenius plots). For the purified, detergent-depleted enzyme a linear relation was obtained. If Triton X-100 was added to the assay medium a curved plot resulted. For acetylcholinesterase incorporated into dimyristoylphosphatidylcholine vesicles a clear break in the plot was observed at the phase transition temperature of the lipid. With lipids not experiencing a phase transition within the temperature range investigated, again a linear relation was obtained. These results show that the activity of human erythrocyte membrane acetylcholinesterase is stroiigly modulated by its hydrophobic environment.

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The amounts of phosphorus and iron in various isolated ferritin preparations were investigated by: chemical analysis on ferritin samples and electron probe X-ray microanalysis on ferritin particles from the same preparations. A high correlation was found between iron to phosphorus ratios obtained by both methods. Further investigation by electron probe X-ray microanalysis on lysosomes of hepatic cells of patients with idiopathic and secondary hemochromatosis revealed lysosomal iron to phosphorus ratios which were very similar in all parenchymal cells but different from ratios obtained in Kupffer cells. Lysosomal iron to phosphorus ratios in hepatocytes did not change after intensive phlebotomy treatment. It is postulated therefore that, during phlebotomy, iron and phosphorus are concomitantly lost from the hepatic lysosomes.