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K J White

Publications and source records attributed to K J White.

10 recordsLinked to original sources
PubMed2003

Distinct recognition of substrates by the human and Drosophila serotonin transporters.

The human and Drosophila serotonin transporters (hSERT and dSERT, respectively) were used to explore differences in substrate properties. hSERT and dSERT showed similar Km values for 5-hydroxytryptamine (5-HT; serotonin) transport (1.2 and 0.9 micro M, respectively), suggesting similar recognition of 5-HT by the two species variants. Although dSERT cell surface expression was approximately 8-fold lower than that of hSERT, dSERT does appear to have a 2-fold faster turnover number for inward transport of 5-HT. Interestingly, another substrate, N-methyl-4-phenylpyridinium (MPP+), was transported only by hSERT. However, MPP+ inhibited 5-HT uptake in both species variants with similar potencies. Two cross-species chimeras, H1-118D119-627 and H1-281D282-476H477-638, were also unable to transport MPP+, implicating the role of transmembrane domains V to IX in the substrate permeation pathway. Based on exchange experiments, certain substituted-amphetamines also appear to be poor substrates at dSERT. Two-electrode voltage-clamp studies in oocytes confirmed that the amphetamines do not possess substrate-like properties for dSERT. Our data suggest distinct molecular recognition among SERT substrate classes that influence translocation mechanisms.

1-Methyl-4-phenylpyridinium↗
PubMed2000

Effects of teacher feedback on the reputations and peer perceptions of children with behavior problems.

We explored whether teacher feedback modified children's preferences and perceptions of a target child with behavior problems. First- and second-grade children (M age = 7.8 years) viewed a videotape of a target actor presented as having a liked, average, or disliked reputation. A second videotape depicted a teacher's verbal responses to the target's behavior as (a) positive, (b) neutral-salient, or (c) corrective. Both salience and valence of teacher feedback were assessed. Main effects of feedback and reputation indicated that feedback had at least minimal effects at each level of the target's reputation. Teacher feedback is discussed with respect to its effects on perceptions of behavior versus affective responses toward behavior-problem children. A significant interaction showed that when combined with a liked reputation, positive and neutral-salient feedback conditions increased the salience and positive evaluation of the target child, thus illustrating the importance of considering nonevaluative teacher attention in combination with children's reputational status.

Child↗
PubMed1993

Social goals: relationship to adolescent adjustment and to social problem solving.

Examined the relations between adolescent boys' social goals of dominance, revenge, avoidance, and affiliation and (1) self-reported negative adolescent outcomes; (2) subjective sense of self-esteem; and (3) externalizing, internalizing, and prosocial behaviors, as rated by peers and teachers. Results indicated that social goal values were related to diverse aspects of self-, teacher-, and peer-reported social and behavioral functioning, with a consistent association found between a range of delinquent, substance-using, and behavioral difficulties, and endorsement of high goal values for dominance and revenge and low goal values for affiliation. Results also indicated that teacher-identified aggressive boys differed from nonaggressive boys in the value they placed on social goals, with aggressive boys placing a higher value on goals of dominance and revenge, and lower value on goals for affiliation. Finally social goal choice had a clear relation to the social problem-solving differences of aggressive and nonaggressive boys.

Adolescent↗
PubMed1992

Existence of a hydrogen sulfide:ferric ion oxidoreductase in iron-oxidizing bacteria.

The existence of a hydrogen sulfide:ferric ion oxidoreductase, which catalyzes the oxidation of elemental sulfur with ferric ions as an electron acceptor to produce ferrous and sulfite ions, was assayed with washed intact cells and cell extracts of various kinds of iron-oxidizing bacteria, such as Thiobacillus ferrooxidans 13598, 13661, 14119, 19859, 21834, 23270, and 33020 from the American Type Culture Collection, Leptospirillum ferrooxidans 2705 and 2391 from the Deutsche Sammlung von Mikroorganismen, L. ferrooxidans BKM-6-1339 and P3A, and moderately thermophilic iron-oxidizing bacterial strains BC1, TH3, and Alv. It was found that hydrogen sulfide:ferric ion oxidoreductase activity comparable to that of T. ferrooxidans AP19-3 was present in all iron-oxidizing bacteria tested, suggesting a wide distribution of this enzyme in iron-oxidizing bacteria.

Journal Article↗
PubMed1991

Mixed ligand complexes of iron with cyanide and phenanthroline as new probes of metalloprotein electron transfer reactivity. Analysis of reactions involving rusticyanin from Thiobacillus ferrooxidans.

A family of 12 different mixed ligand complexes of iron with cyanide and substituted 1,10-phenanthroline was prepared. The electron transfer properties of each reagent were systematically manipulated by varying the substituent(s) on the aromatic ring system and the stoichiometry of the two types of ligands in the complex. Values for the standard reduction potentials of each member of this family of electron transfer reagents were determined and spanned from 500 to 900 mV. The one-electron transfer reactions between each of these substitution-inert reagents and the high potential blue copper protein, rusticyanin, from Thiobacillus ferrooxidans were studied by stopped flow spectrophotometry under acidic conditions. For comparison with the protein results, the kinetics of electron transfer between each of these reagents and sulfatoiron were also investigated. The Marcus theory of electron transfer was successfully applied to this set of kinetic data to demonstrate that 10 of the 12 reagents had equal kinetic access to the redox center of the rusticyanin and utilized the same reaction pathway for electron transfer. The utility of these synthetic electron transfer reagents in characterizing the electron transfer properties of very high potential, redox-active metalloproteins is illustrated.

Azurin↗
PubMed1991

Effect of divers anions on the electron-transfer reaction between iron and rusticyanin from Thiobacillus ferrooxidans.

Rusticyanin is a soluble blue copper protein found in abundance in the periplasmic space of Thiobacillus ferrooxidans, an acidophilic bacterium capable of growing chemolithotrophically on soluble ferrous sulfate. The one-electron-transfer reactions between soluble iron and purified rusticyanin were studied by stopped-flow spectrophotometry in acidic solutions containing each of 14 different anions. The second-order rate constants for both the Fe(II)-dependent reduction and the Fe(III)-dependent oxidation of the rusticyanin varied as a function of the identity of the principal anion in solution. Analogous electron-transfer reactions between soluble iron and bis(dipicolinato)cobaltate(III) or bis(dipicolinato)ferrate(II) were studied by stopped-flow spectrophotometry under solution conditions identical with those of the rusticyanin experiments. Similar anion-dependent reactivity patterns were obtained with soluble iron whether the other reaction partner was rusticyanin or either of the two organometallic complexes. The Marcus theory of outer-sphere electron transfer reactions was applied to this set of kinetic data to demonstrate that the rusticyanin may possess at least two electron-transfer pathways for liganded iron, one where the pattern of electron-transfer reactivity is controlled largely by protein-independent activation parameters and one where the protein exhibits an anion-dependent kinetic specificity. The exact role of rusticyanin in the iron-dependent respiratory electron transport chain of T. ferrooxidans remains unclear.

Anions↗
PubMed1990

Ca2+ redistribution from bound to free form is required for tumor necrosis factor actions in 30A5 preadipocytes.

Tumor necrosis factor/cachectin (TNF) inhibits differentiation of 30A5 preadipocytes into adipocytes. In this process, TNF inhibits the expression of the gene for acetyl-coenzyme-A carboxylase, the rate-limiting enzyme for biogenesis of long chain fatty acids. One of the early reactions caused by TNF is the Ca2+ redistribution of Ca2+ from the bound form to the free form. This Ca2+ redistribution results in a transient Ca2+ efflux. High concentrations of Mg2+ inhibit Ca2+ redistribution and efflux. This inhibition reverses the repression of acetyl-coenzyme-A carboxylase and reverses the TNF inhibition of the differentiation of 30A5 preadipocytes into adipocytes. This indicates that Ca2+ redistribution between the bound and the free form is an obligatory event in the sequence of actions caused by TNF in 30A5 cells.

Acetyl-CoA Carboxylase↗