Characteristics of the interaction between 2-alkylmalonates and the substrate-binding site of the dicarboxylate carrier of rat liver mitochondria

The effect of thirteen synthetic 2-n-alkyl derivatives of malonic acid on the rate of the mitochondrial succinate oxidase reaction controlled by the dicarboxylate carrier, was studied. These compounds were shown to act as competitive inhibitors of succinate transport and could interact with the carrier according to the 1:1 stoichiometry. The affinity of the inhibitor for the carrier increased in parallel with the increase in the alkyl residue length. This dependence was impaired only in the case of pentyl-, hexyl- and heptylmalonates having close values of inhibition constants. The data obtained suggest that the polar site and two hydrophobic regions are located in the vicinity of the carrier active site. The possible organization of the carrier substrate-binding site is discussed.     

Dual action of hydroxylated diphenylethylene estrogens on protein kinase C1

Protein kinase C (PKC) I (gamma), II (beta) and III (alpha) subspecies are all activated by 1,1-di-(p-hydroxyphenyl)ethylene derivatives (DPE) at micromolar concentrations. This PKC activation depends on the presence of both Ca2+ and phosphatidylserine (PS) but does not require diacylglycerol (DG). DPEs enhance PKC activity at low PS concentrations, but not at saturating PS concentrations. Like DG, DPEs increase the apparent affinity of PKC for PS as well as for Ca2+, but lead to a decrease in the catalytic activity (Vmax). In the presence of saturating DG concentrations, DPEs exhibit an inhibitory action. The derivatives also inhibit the activity of the proteolytic fragment of PKC, protein kinase M. It is concluded that DPEs are mixed-type inhibitors, probably interacting with the catalytic domain of the enzyme.     

Hepatotrophic growth factor in blood of mice treated with carbon tetrachloride

The presence of a human hepatocyte growth factor (hHGF)-like DNA-synthesis promoter in platelet-poor serum of mice with liver injury was examined. Activity of the serum for stimulating DNA synthesis in cultured rat hepatocytes was low in untreated or vehicle-treated mice, but markedly increased 24 h after carbon tetrachloride administration and then dropped to normal levels prior to the peak of liver DNA synthesis. The effect of the serum was additive with the maximal effects of mouse and human epidermal growth factors, but not with that of hHGF. The growth-stimulating factor in the mouse serum, like hHGF, had affinity for heparin and was heat-labile. These results indicate that the level of a serum hHGF-like hepatocyte growth factor increased in mice treated with carbon tetrachloride prior to liver regeneration.     

Light-induced Activation of Electrogenic H+ Extrusion and K+ Uptake in Elodea densa Depends on Photosynthesis and is Mediated by the Plasma membrane H+ ATPase

In Elodea densa leaves light strongly stimulates electrogenic,K ⁺-dependent, vanadate- and erythrosin B-sensitive H⁺ extrusionand hyperpolarizes the transmembrane electrical potential. Theseeffects of light are suppressed by treatment with DCMU, an inhibitorof photosynthesis, which has no effect on H⁺ extrusion in thedark. Light-induced H⁺ extrusion requires the presence of K⁺in the medium and is associated with increased K⁺ uptake andalkalinization of the cell sap. Light-induced H⁺ extrusion increaseswith increased CO₂ concentration. At constant CO₂ concentration(10⁴ parts 10^–6) the rate of H⁺ extrusion is stronglyenhanced by an increased light intensity up to 30 W m^–2.Different wavelengths, between 400 and 730 nm, induce a significantstimulation of both proton secretion and transmembrane potentialhyperpolarization. The stimulating effects of light on H⁺ extrusion, K⁺ uptakeand cell sap pH are very similar to those induced in the darkby fusicoccin, a toxin known to stimulate strongly ATP-driven,vanadate- and erythrosin B-sensitive H⁺ transport. In the light,the effects of fusicoccin are only partially additive to thoseof light, thus suggesting that the two factors influence thesame system. The identification of this system with the plasmamembrane H⁺-ATPase is indicated by the observed inhibition ofthe effects of either light or fusicoccin by the H⁺-ATPase inhibitorsvanadate and erythrosin B. These data indicate that the activation of electrogenic H⁺ extrusionand of K⁺ uptake by light is mediated by some products of photosynthesis.The mechanism and the possible physiological implications ofthis phenomenon are discussed. Key words: Photosynthesis, H⁺ pump, K⁺ uptake, Elodea densa     

Dietary salt intake and its relevance to ionic regulation in freshwater salmonids

Dietary sodium intake for freshwater salmonids feeding in the wild (invertebrate diet) or in captivity (pellet diet) was calculated and compared with published branchial sodium influx values. Dietary sodium intake (mmol kg⁻¹ per month) increases from winter minimum values of 5 and 30-40 to reach maximum values in summer of 175 and 240 for invertebrate and pellet diet, respectively. In summer, dietary sodium intake for fish feeding in the wild was of the same magnitude as branchial sodium influx. The implications of dietary sodium intake for sodium balance in freshwater fish are discussed.     

Chemotropism and branching as alternative responses of Achlya bisexualis to amino acids

Hyphae of Achlya bisexualis growing on lean media orient their extension towards a source of amino acids, and also put forth branches. Micropipettes were used to generate gradients of amino acids in the vicinity of individual hyphae. Phenylalanine and methionine were the most powerful attractants: 0.04 mM amino acid in the pipette produced reorientation, and higher concentrations made the hyphae curl around the pipette and grow into its tip. Hyphae detected gradients as low as 5% across their width. Methionine and phenylalanine appeared to bind to different receptors. Local application of these amino acids also elicited the emergence of single branches, next to the pipette and on the high side of the gradient; comparison of diverse amino acids and their analogues suggested that branching and chemotropism share common receptors. By contrast, cytochalasin A and various ionophores induced branches at random sites, without receptor involvement. We propose that binding of amino acids to their receptors determines the site of precursor vesicle exocytosis, and consider possible mechanisms.     

The use of ethidium bromide to assess a novel injury/recovery phenomenon in Listeria monocytogenes in inhibitory NaCl conditions

An injury and recovery phenomenon was observed in Listeria monocytogenes inoculated into a medium containing 2·2 mmol l⁻¹ NaCl, a concentration that was inhibitory to growth. The apparent loss then recovery of viability, as determined by plate counts, was compared with the uptake of ethidium bromide by the cells and found to be inversely related. Injury was caused not only by the initial osmotic up-shock but also by the subsequent down-shock involved in the spread plate protocol.