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Active transport of calcium ions has been demonstrated in inside-out membrane vesicles from Mycobacterium phlei mediated by respiratory linked substrates as well as by ATP hydrolysis. The uptake of calcium exhibited an apparent K , of 80 pM and V of 16.6 nmol calcium uptake x min-' x mg protein-'. A fortyfold concentration gradient for calcium ions was calculated for both the ATP-induced and the respiration-induced transport of calcium. Removal of coupling-factor-latent ATPase resulted in the complete loss of ATP-driven Ca2+ transport whereas the respiration-driven uptake was reduced by 40-50 %. The uptake of calcium was inhibited by the proton conducting ionophores carbonylcyanide m-chlorophenylhydrazone and Gramicidin-D. The accumulated calcium was freely exchangeable with external calcium and was rapidly released by the addition of inhibitors of energy transduction, proton-translocating uncouplers or the ionophore A231 87. The uptake of the weak base, methylamine, upon the oxidation of respiratory-linked substrates or the hydrolysis of ATP showed the generation of a proton gradient (inside acidic) which was partially collapsed on the addition of calcium ions. These results suggest that a Ca2+/H+ antiport mechanism may be responsible for the transport of calcium.Electron transport particles prepared by the sonication of Mycobacteriurnphlei cells, are capable of oxidation with succinate or NAD+-linked substrates [I] and also exhibit phosphorylation coupled to the substrate oxidation. However, removal of coupling-factor-latent ATPase from the membrane vesicles by washing with 0.25 M sucrose, results in the formation of depleted vesicles which exhibit only substrate oxidation but no coupled phosphorylation [2,3]. The latent ATPase is activated by trypsin treatment and requires the presence of Mg2+ for the expression of its ATPase activity [4,5]. Unlike membrane-bound ATPase from Escherichiu coli [6] and Micrococcus lysodeikiticus [7], the M . phlei latent ATPase did not show any calciumstimulated ATPase activity [4]. Therefore, it was of interest to ascertain whether in spite of this, the membrane vesicles from M . phlei are capable of transportThis paper is dedicated to the 80th Birthday of Dr Fritz Lipmann.Abbreviations and Trivial Names. Membrane vesicles, electron transport particles; depleted vesicles, electron transport particles depleted of coupling-factor-latent ATPase; Hepes, 4-(2-hydroxyethyl)-l-piperazineethanesulfonic acid; ansyl, 8-aninlino-l-naphthalenesulfonic acid; Ph (NMez)2,N,N,N',N'-tetrarnethyl-p- [12]. It was also found desirable to study the mechanism of calcium transport and its effect on oxidative phosphorylation in M . phlei membrane vesicles.The present communication described the properties and characteristics of calcium transport in M . phlei membrane vesicles. It has been demonstrated that the oxidation of the respiratory-linked substrates or the hydrolysis of ATP generate a proton gradient of approximately 2.0 pH units across the membrane (inside acidic) which presumably provides th...

The accumulation of several amino acids in the acid-soluble fraction and their incorporation into protein in rat liver parenchymal cell suspensions, has been shown to depend on the concentration of cells in the incubation medium; the uptake, both in the acid-soluble and the acid-insoluble fractions, decreased as the cell concentration increased from 0.03 X 10(6) cells/ml upwards, reaching a plateau at high cell concentrations (3-5 X 10(6) cells/ml). The uptake values at high cell concentrations were the same as those obtained in liver slices in which a similar effect was not observed. Evidence is presented which suggests that this phenomenon is mediated by a material released from the cells in suspension, which is inhibitory to enhancement of the uptake of amino acids by these cells over and above the value obtained in normal, adult liver slices.

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