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J L Howland

Publications and source records attributed to J L Howland.

At least 19 recordsLinked to original sources
PubMed1991

Uptake of inorganic pyrophosphate by Bacillus megaterium.

Cells of Bacillus megaterium take up inorganic pyrophosphate, employing a saturable carrier which is sensitive to sulfhydryl reagents, orthophosphate, and arsenate. Uptake is stimulated by proton ionophores, including CCCP and nigericin, indicating that proton cotransport can lead to an opposing gradient. Inhibitor sensitivity, as well a relatively high Km for inorganic pyrophosphate render it likely that uptake is mediated by an orthophosphate transport system.

Bacillus megaterium↗
PubMed1985

Influence of anion flux upon mitochondrial oxidative phosphorylation.

We have measured mitochondrial ATP synthesis during passive anion influx and find that influx of phosphate leads to diminished efficiency (as reflected in the ATP:0 ratio) whereas influx of acetate produced enhanced efficiency. The anions, sulfate, propionate, and thiocyanate, are without influence on the ATP:0 ratio. It is likely that the opposite effects of phosphate and acetate on the ATP:0 ratio reflect phosphate-acetate exchange, and that acetate influx produces its positive effect on ATP synthesis by promoting phosphate efflux. Thus, phosphate efflux may be associated with increased, and phosphate influx, with decreased energy conservation.

Acetates↗
PubMed1985

Evidence for the ordered release of rubidium ions occluded within the Na,K-ATPase of mammalian kidney.

When Na,K-ATPase containing occluded rubidium ions is exposed to orthophosphate, in the presence of magnesium ions, there is a rapid release of half or all of the occluded ions. This behaviour is observed irrespective of whether the occluded-rubidium form of the enzyme is generated by putting the unphosphorylated enzyme in a sodium-free medium containing rubidium ions, or by allowing rubidium ions to catalyse the hydrolysis of phosphoenzyme made by adding ATP to enzyme suspended in a medium containing sodium and magnesium ions. The release of occluded rubidium ions by orthophosphate requires the presence of magnesium, presumably because phosphorylation is necessary. Whether the addition of orthophosphate causes the rapid release of all or of half of the occluded rubidium depends on whether free rubidium (or potassium, thallium or (probably) caesium ions) are present in the medium at the time the orthophosphate is added. In the absence of free ions of these species, all of the occluded rubidium is released. In their presence (in adequate concentration), only half of the occluded rubidium is released. The relative effectiveness of the different potassium congeners in preventing the rapid release of 50% of the occluded rubidium when orthophosphate is added is: thallium greater than rubidium greater than potassium greater than caesium. Lithium and sodium are ineffective even at high concentrations, and sodium ions strongly antagonize the effect of free rubidium ions. In a sodium-free, Tris medium, the concentration of free rubidium ions necessary for a half-maximal effect is about 30 microM. In a medium containing 250 microM-free rubidium, the concentration of sodium necessary to reduce the effect of free rubidium by 50% is about 500 microM. These figures are compatible with the hypothesis that the free rubidium or other ions act at the potassium-loading sites at the extracellular face of the pump. By starting with enzyme occluding unlabelled rubidium, and using 86Rb-labelled free rubidium, it is possible to show that the free ions that prevent the rapid release of half of the occluded ions themselves become occluded. These experiments are significant in two ways. First, they provide direct evidence for the existence of a second route for the release of occluded rubidium (and therefore presumably of occluded potassium) ions. Secondly, they seem to require that the release of occluded ions by this route occurs in an ordered fashion.

Animals↗
PubMed1984

Inhibition of erythrocyte plasma membrane NADH dehydrogenase by nucleotides and uncouplers.

Erythrocyte ghost NADH dehydrogenase is inhibited in a competitive fashion by ATP and ADP whereas other nucleoside di- and triphosphates, cyclic nucleosides, as well as non-phosphorylating ATP analogs are relatively ineffective. In addition, this enzyme, measured with ferricyanide as electron acceptor, is inhibited by uncouplers of oxidative phosphorylation (proton-conducting reagents), the inhibition being competitive in character (i.e., the uncouplers were without influence upon maximum velocity). The effectiveness of the uncouplers was in the order of their hydrophobic character with the presence of the alkyl side chain rendering nonyl-dinitrophenol much more active than 2,6-dinitrophenol itself. Hydrophobic compounds that are not protonophores (e.g., eosin, proflavin or valinomycin) were not inhibitory. Whereas adenine nucleotides probably inhibit NADH oxidation competitively through structural similarity with the substrate, it appears unlikely that uncouplers compete at the NADH site directly. Rather, the apparently-competitive inhibition in the latter case may reflect competition for proton transfer to an acceptor residing in a hydrophobic region of the enzyme complex.

Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone↗
PubMed1984

Sphingolipid metabolism during infection of human fibroblasts by herpes simplex virus type 1.

Results from several experiments support the view that sphingomyelin turnover and glycosphingolipid synthesis play a role in herpes simplex virus infection of cells in culture. Inhibition of sphingomyelinase by phosphatidylcholine or by a synthetic ceramide, N-palmitoyl-DL-dihydrosphingosine, interferes substantially with virus reproduction as does a genetic defect in the enzyme (Niemann-Pick disease). In Niemann-Pick cells, yields of infectious virus are about 3% of the normal level. An inhibitor of ceramide: UDP glucose glucosyltransferase was also used to test the effect of altered glycosphingolipid synthesis on infection. This compound, DL-2-decanoylamino-3-morpholinopropiophenone, decreased virus yields to a level about 0.1% of normal at the highest concentration tested.

Cells, Cultured↗
PubMed1981

Incorporation of 32P-phosphate into membrane phospholipids during infection of cultured human fibroblasts by herpes simplex virus type 1.

Infection of cultured human skin fibroblasts by herpes simplex virus leads to increased incorporation of labeled inorganic phosphate into host membrane sphingomyelin. Incorporation into the other major membrane phospholipids, including phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and phosphatidylserine, was unaffected. Since sphingomyelin has been shown to serve as precursor to ceramides (via sphingomyelinase) in monkey kidney cells and since enhanced synthesis of ceramide-based glycolipids has been shown to occur after herpes simplex virus infection, we suggest that the observed increase in labeling of sphingomyelin may reflect mobilization for glycolipid synthesis. The distribution of phosphate label among the phospholipids of the viral envelope was identical to that among the phospholipids of the cellular cytoplasmic membrane fraction and differed from that of the nuclear fraction.

Cells, Cultured↗
PubMed1978

Energy coupling in liver mitochondria from dystrophic mice: differential sensitivity of oxidative phosphorylation and Ca2+ uptake to K+.

Studies were carried out to examine oxidative phosphorylation, cation uptake, and electrokinetic properties of liver mitochondria from genetically dystrophic mice in comparison with those from livers of littermate controls. While no differences were seen with respect to the rates of substrate oxidation, ADP/oxygen ratio, and RCl and cytochrome content, the mitochondria from the dystropic group were characterized by an elevated basal ATPase activity in the presence of NaCl. Additionally, these mitochondria were highly sensitive to high concentrations of exogenously added K+ that, besides stimulating state 4 respiration, caused uncoupling in the mitochondria. These mitochondria accumulated Ca2+ at a higher rate, and unlike the controls, Ca2+ uptake was not sensitive to exogenously added K+. It was also observed that the net negative charge on mitochondria decreased significantly in the dystrophic state. It is thus apparent that muscular dystrophy manifests itself also in terms of alteration in the membrane properties of liver mitochondria.

Adenosine Diphosphate↗
PubMed1977

Erythrocyte lipids in heterozygous carriers of duchenne muscular dystrophy.

Erythrocyte membranes from heterozygous carriers of Duchenne muscular dystrophy exhibit a diminished amount of palmitoleic acid when compared to membranes from normal subjects. A similar, but more variable, diminution is observed in the case of patients with this disorder. The change in fatty acid composition appears related to a low membrane triglyceride content and may provide both a possible technique for carrier detection and a clue regarding pathogenesis.

Erythrocyte Membrane↗
PubMed1976

Erythrocyte surface membrane alterations.

Electrophoretic mobility measurements were made of red blood cells obtained from patients with Duchenne and myotonic muscular dystrophy, from dystrophic mice and chickens, and from corresponding controls. Alterations in the erythrocyte surface electrokinetic properties were found in dystrophic mice and chickens and in many, but not all, patients with muscular dystrophy. The results are consistent with the concept of muscular dystrophy as a systemic membrane disease not limited to muscle.

Adolescent↗
PubMed1974

Erythrocyte deformation in human muscular dystrophy.

Erythrocytes from patients with congenital muscular dystrophy exhibit dramatic surface deformation when observed with a scanning electron microscope. A similar alteration, but one affecting a smaller proportion of cells, occurs in the case of female carriers of the sex-linked Duchenne dystrophic condition. These observed changes in the erythrocyte surface may reflect a systemic defect in membrane properties.

Adolescent↗