Interaction of vanadate with membrane-bound ATPase from Mycobacterium phlei

Vanadate inhibited the formation of proton gradient and membrane potential as well as Ca2+ transport by everted membrane vesicles from Mycobacterium phlei, with half-maximal inhibition occurring at 5 to 14 microM. That this is due to the inhibition of the proton-translocating ATPase was suggested by the observation that the inhibition described above occurred only when the processes were driven by the hydrolysis of ATP but not when energized by the oxidation of succinate and NADH. Furthermore, vanadate did indeed inhibit ATP hydrolysis by these membrane vesicles. Although the inhibition of ATP hydrolysis could be demonstrated only in the presence of high concentrations (e.g. 11 mM) of Mg2+, this was presumably due to the fact that we were measuring the sum of ATP hydrolysis by both coupled and partially uncoupled enzymes. This is the first reported effect of vanadate on bacterial proton-translocating ATPase.     

Selective 19-hydroxylase inhibition by an aromatase inhibitor, 4-hydroxyandrostenedione

19-Nor-deoxycorticosterone is a newly recognized mineralocorticoid which has been associated with some forms of genetic, experimental, and human hypertension. To further examine this relationship, specific inhibitors of 19-nor-deoxycorticosterone biosynthesis must be developed. Since 19-hydroxylation is the pivotal step in both 19-nor-deoxycorticosterone biosynthesis and aromatization of androgens to estrogens, we evaluated an aromatase inhibitor, 4-hydroxyandrost-4-ene-3,17-dione on the inhibition of 19-hydroxylation in both rat and human adrenal mitochondria in vitro and 19-nor-deoxycorticosterone production and blood pressure in spontaneously hypertensive rats in vivo. Adrenal mitochondria from 48 male Sprague-Dawley rats and 1 patient with an aldosterone-producing adenoma were incubated in the presence of deoxycorticosterone substrate both with and without 4-hydroxyandrost-4-ene-3,17-dione. 4-Hydroxyandrost-4-ene-3,17-dione produced significant inhibition of 19-hydroxy-deoxycorticosterone production in both rat and human adrenal mitochondria, with a smaller and not significant inhibition of corticosterone and 18-hydroxy-corticosterone. 4-Hydroxyandrost-4-ene-3,17-dione given subcutaneously to spontaneously hypertensive rats lowered 19-nor-deoxycorticosterone by 69% and completely abolished hypertension compared to Wistar-Kyoto controls. These data demonstrate that 4-hydroxyandrost-4-ene-3,17-dione is a specific inhibitor of 19-hydroxylase, that it lowers 19-nor-deoxycorticosterone production and prevents hypertension in the spontaneously hypertensive rat. These studies reinforce the possible pathogenic significance of 19-nor-deoxycorticosterone in hypertension in spontaneously hypertensive rats.     

Inactivation of cephalothin and cephaloridine by Staphylococcus aureus

Benner, Ernest J. (University of Washington School of Medicine, Seattle), John V. Bennett, Jean L. Brodie, and William M. M. Kirby. Inactivation of cephalothin and cephaloridine by Staphylococcus aureus. J. Bacteriol. 90:1599-1604. 1965.-Marked differences were observed in the susceptibility of penicillinase-producing staphylococci to cephalothin and cephaloridine. All of 100 strains of penicillin G-resistant Staphylococcus aureus, with the use of a large inoculum, were found to be susceptible to 2 mug/ml of cephalothin, whereas only 50% were susceptible to this concentration of cephaloridine, and 15% required 15 mug/ml or more for inhibition. In contrast, penicillin G-sensitive strains were more susceptible to cephaloridine and did not show the marked inoculum effect observed with the cephaloridine-resistant strains. These differences were due to a much greater destruction of cephaloridine than of cephalothin by staphylococcal penicillinase. Cephaloridine-resistant staphyloccoci were stronger penicillinase producers than were susceptible strains, and the resistant strains were found to inactivate cephaloridine by hydrolysis of the beta-lactam ring. In population studies, cephaloridine-resistant cells differed from methicillin-resistant cells in that they decreased in numbers as the drug concentration was increased, and the survivors in higher drug concentrations were no more resistant than was the parent strain. Treatment with acriflavine eliminated resistance of the cells to both penicillin G and cephaloridine. It was concluded that cephaloridine resistance was due to hydrolysis by penicillinase, and that this was related to the pyridine ring substitution in the cephalosporanic acid nucleus.     

Anion binding by human lactoferrin: results from crystallographic and physicochemical studies.

The anion-binding properties of lactoferrin (Lf), with Fe3+ or Cu2+ as the associated metal ion, have been investigated by physicochemical and crystallographic techniques. These highlight differences between the two sites and in the anion-binding behavior when different metals are bound. Carbonate, oxalate, and hybrid carbonate-oxalate complexes have been prepared and their characteristic electronic and EPR spectra recorded. Oxalate can displace carbonate from either one or both anion sites of Cu2(CO3)2Lf, depending on the oxalate concentration, but no such displacement occurs for Fe2(CO3)2Lf. Addition of oxalate and the appropriate metal ion to apoLf under carbonate-free conditions gives dioxalate complexes with both Fe3+ and Cu2+, except when traces of EDTA remain associated with the protein, when hybrid complexes M2(CO3)(C2O4)Lf can result. The anion sites in the crystal structures of Fe2(CO3)2Lf, Cu2-(CO3)2Lf, and Cu2(CO3)(C2O4)Lf, refined at 2.2, 2.1, and 2.2 A, respectively, have been compared. In every case, the anion is hydrogen bonded to the N-terminus of helix 5, an associated arginine side chain, and a nearby threonine side chain. The carbonate ion binds in bidentate fashion to the metal, except in the N-lobe site of dicupric lactoferrin, where it is monodentate; the difference arises from slight movement of the metal ion. The hybrid complex shows that the oxalate ion binds preferentially in the C-lobe site, in 1,2-bidentate mode, but with the displacement of several nearby side chains. These observations lead to a generalized model for synergistic anion binding by transferrins.     

Visualizing and quantifying natural selection

Modern methods of analysis are enabling researchers to study natural selection at a new level of detail. Multivariate statistical techniques can Identify specific targets of selection and provide parameter estimates that fit into equations for evolutionary change. A more Intuitive understanding of the form of selection can be provided through graphical representation of selection surfaces. Combinations of quantitative and visual analyses are providing researchers with new insights into the details of natural selection in the wild.