The chloride requirement for photosynthetic oxygen evolution. Analysis of the effects of chloride and other anions on amine inhibition of the oxygen-evolving complex

In the presence of Cl^?, the severity of ammonia-induced inhibition of photosynthetic oxygen evolution is attenuated in spinach thylakoid membranes (Sandusky, P.O. and Yocum, C.F. (1983) FEBS Lett. 162, 339–343). A further examination of this phenomenon using steady-state kinetic analysis suggests that there are two sites of ammonia attack, only one of which is protected by the presence of Cl^?. In the case of Tris-induced inhibition of oxygen evolution only the Cl^? protected site is evident. In both cases the mechanism of Cl^? protection involves the binding of Cl^? in competition with the inhibitory amine. Anions (Br^? and NO^?₃) known to reactive oxygen evolution in Cl^?-depleted membranes also protect against Tris-induced inhibition, and reactivation of Cl^?-depleted membranes by Cl^? is competitively inhibited by ammonia. Inactivation of the oxygen-evolving complex by NH₂OH is impeded by Cl^?, whereas Cl^? does not affect the inhibition induced by so-called ADRY reagents. We propose that Cl^? functions in the oxygen-evolving complex as a ligand bridging manganese atoms to mediate electron transfer. This model accounts both for the well known Cl^? requirement of oxygen evolution, and for the inhibitory effects of amines on this reaction.     

Comparative Cytochrome Oxidase and Superoxide Dismutase Analyses on Strains of Azotobacter vinelandii and Other Related Free-Living Nitrogen-Fixing Bacteria

Quantitative N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) oxidase and superoxide dismutase (SOD) analyses were performed on representative organisms of the family Azotobacteraceae. Azotobacter vinelandii, Azotobacter chroococcum, Azotobacter paspali, and Derxia gummosa exhibited high quantitative TMPD oxidase activities, and their extracts possessed very active and electrophoretically homogeneous (single gel band) Fe-type SODs. Azomonas macrocytogenes extracts had similar single Fe-type SODs, and their cells exhibited no TMPD-dependent cytochrome oxidase activity. Nitrogen-fixing cells of Beijerinckia indica, Beijerinckia derxii, and Beijerinckia mobilis exhibited minimal TMPD oxidation capabilities (rates equivalent to the TMPD autooxidation reaction), and these extracts also possessed very active SODs but only of the Mn metallotype.     

Glycogen synthesis by cell-free extracts from the dimorphic yeast Candida albicans

A particulate glucosyltransferase prepared from budding and filamentous cultures of Candida albicans used uridine diphosphate glucose as sole glucosyl donor in a reaction (measured by following the incorporation of [¹⁴C]-glucose from UDP [¹⁴C]-glucose into polymer) stimulated by glucose-6-phosphate and inhibited by adenosine triphosphate and guanosine triphosphate. The radiolabelled reaction product was solubilized by -amylase, and, on oxidation with periodate followed by reduction with borohydride and acid hydrolysis, yielded erythritol and glycerol in the ratio of 4 to 1. The radiolabelled glucosyl residues were attached to an endogenous acceptor of high molecular weight.     

Biochemical genetics of aldehyde dehydrogenase isozymes in the mouse: Evidence for stomach- and testis-specific isozymes

Electrophoretic and activity variants have been observed for stomach and testis aldehyde dehydrogenases, respectively, among inbred strains of the house mouse (Mus musculus). Genetic evidence was obtained for two new loci encoding these isozymes (designated Ahd-4 and Ahd-6, respectively, for the stomach and testis isozymes) which segregated independently of a number of mouse gene markers, including Ahd-1 (encoding mitochondrial aldehyde dehydrogenase) on chromosome 4, ep (pale ears), a marker for chromosome 19, on which Ahd-2 (encoding liver cytosolic aldehyde dehydrogenase) has been previously localized, and Adh-3 (encoding the stomach-specific isozyme of alcohol dehydrogenase) on chromosome 3. Recombination studies have indicated, however, that Ahd-4 and Ahd-6 are distinct but closely linked loci on the mouse genome. An extensive survey of the distribution of Ahd-1, Ahd-2, Ahd-4, and Ahd-6 alleles among 56 strains of mice is reported. No variants have been observed, so far, for the microsomal (AHD-3) and mitochondrial/cytosolic (AHD-5) isozymes previously described. This study, in combination with previous investigations on mouse aldehyde dehydrogenases, provides evidence for six genetic loci for this enzyme.     

Regulation of human leukocyte microsomal hydroxymethylglutaryl-CoA reductase activity by a phosphorylation and dephosphorylation mechanism

The activity of microsomal 3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.34), obtained from cultured human IM-9 lymphoid cells or freshly isolated human peripheral blood leukocytes, is modulated by a phosphorylation/dephosphorylation mechanism. Addition of MgATP + ADP to IM-9 cell microsomal reductase leads to a time-dependent loss of enzyme activity. Inactivated reductase is reactivated by rat liver reductase phosphatase. Kinase-dependent IM-9 cell microsomal reductase, prepared by heating IM-9 microsomes for 15 min at 50°C, is inactivated in the presence of MgATP and ADP only after addition of cytosolic reductase kinase from either IM-9 cells, freshly isolated leukocytes or rat liver. Inactivation is time-dependent and dependent on the cytosolic protein concentration. Inactivated reductase is reactivated by rat liver reductase phosphatase. For cultured IM-9 cells and freshly isolated leukocytes incubated with culture medium for 2 h, the ratios of active (unphosphorylated) to total (phosphorylated + unphosphorylated) reductase activity are 0.22 and 0.43, respectively. Thus, in addition to its regulation by changes in the amount of total enzyme protein, human leukocyte reductase activity is also modulated by a phosphorylation/dephosphorylation mechanism.     

Transglutaminase and receptor-mediated endocytosis in macrophages and cultured fibroblasts

Summary The function of intracellular transglutaminases remains to be clarified. In fibroblasts the links between the activity of this enzyme and receptor-mediated endocytosis are complex and open to interpretation. However, the issue cannot be firmly laid to rest until the structural specificity of the alkylamine inhibitors of endocytosis is explained. In macrophages, there is substantial evidence that the enzyme plays some role in receptor-mediated phagocytosis, but what this role is and how it might relate to endocytosis in other types of cells is at present an unresolved issue.     

Visual unit,EEG and sustained potential shift responses to biologically significant stimuli in the brain of toads (Bufo bufo)

Summary Visual unit activity, EEG changes and sustained potential shifts (SPS) were recorded from the toad tectum whilst the animal was presented with a visual stimulus. Telencephalic EEGs were also recorded.On the surface of the tectum, retinal unit activity preceded a sustained negative shift in potential and an increase in the amplitude and dominant frequency of the EEG. In deeper layers of the tectum, T5 units with configurational selectivity for wormlike stimuli were found. The activity of these units followed a pronounced SPS and EEG change.Visual unit activity was most pronounced during the negative-going phase of the synchronised EEG, when there was also a small decrease in amplitude of neuronal spikes. Similarities between the latencies and durations of EEGs and SPSs, and their response decrements, on repeated stimulus presentation, implies a close relationship between them not shared by the visual units studied. The specific activity of tectal units is discussed in relation to the correlated EEG and SPS changes, which may form part of an adaptive sensitizing mechanism.Abbreviations EEG electroencephalogram - ERF excitatory receptive field - SPS sustained potential shift - T4, T5 tectal neurons