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R D Pratt

Publications and source records attributed to R D Pratt.

28 records · Page 2Linked to original sources
PubMed1989

Inhibition of Na+-dependent phosphate transport by group-specific covalent reagents in rat kidney brush border membrane vesicles. Evidence for the involvement of tyrosine and sulfhydryl groups on the interior of the membrane.

The effects of tyrosine- and sulfhydryl-specific reagents on the Na+-dependent transport of phosphate in brush border membrane vesicles prepared from rat renal cortex were investigated. This study is the first to show that the tyrosine-specific reagents 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole and tetranitromethane inactivate the transporter in a concentration- and time-dependent fashion while the membrane impermeant tyrosine reagent, N-acetylimidazole, has no effect on phosphate uptake. The membrane permeant sulfhydryl reagent N-ethylmaleimide also caused a time- and concentration-dependent inactivation of this transport process but the membrane impermeant reagents 7-chloro-4-sulfobenzo-2-oxa-1,3-diazole and eosin-5-maleimide had little effect on phosphate uptake. The inhibitory effects of both tyrosine- and sulfhydryl-specific reagents were additive, but no protection from inactivation by tyrosine-specific reagents could be achieved by preincubation of the vesicles with the substrates of the transporter or with competitive inhibitors of the transport process. These results suggest that the amino acids modified by these agents are located either within the membrane or on the cytosolic surface of the transporter. These residues may not participate in substrate binding, but may be important for the conformational change of the transporter necessary for the translocation of phosphate across these membranes. This study also shows that Na+-dependent phosphate transport can be inactivated by other reagents which covalently modify histidine, carboxyl, and amino groups on proteins.

4-Chloro-7-nitrobenzofurazan↗
PubMed1989

Post-natal patterns of plasma androgen-binding activity in Djungarian (Phodopus sungorus) and golden (Mesocricetus auratus) hamsters.

The binding of sex steroids to plasma proteins was examined in post-natal Djungarian and golden hamsters. With dihydrotestosterone or testosterone as ligands, steady-state polyacrylamide gel electrophoresis revealed 2 androgen binding components in the plasma of young Djungarian hamsters of both sexes. The fast-moving component exhibited a low affinity and high capacity for androgens and corresponded to albumin in stained gels. In contrast, the slow moving component was a beta-globulin with high affinity (Ka = 10(9) M-1) and low capacity for androgens, and was identified as a specific sex steroid-binding protein (SBP; also SHBG). This SBP did not bind oestrogens or corticosteroids and was electrophoretically distinct from corticosteroid-binding globulin (CBG). In addition, this protein did not appear to be of testicular origin because it was present in immature females and in immature males that had been castrated for 8 days. Plasma concentrations of SBP in males as measured by a diethyl-aminoethyl-cellulose binding assay were low at birth, became significantly elevated shortly thereafter when plasma androgen values were also elevated, and subsequently fell to low levels during puberty. These changes follow the same general pattern that has been described for other mammals, including humans, during this period of reproductive development. Although the significance of elevated SBP concentrations during prepuberty has yet to be determined, it appears that the increased concentrations of high-affinity androgen binding in the plasma of Djungarian hamsters plays a role in the asynchronous pubertal development of the testes and accessory organs which occurs in this species. The post-natal SBP pattern in females was similar to that observed in males. Plasma SBP levels were low or undetectable in adults of both sexes. As previously described for adult golden hamsters, the plasma of post-natal male and female golden hamsters lacked a specific SBP: androgen binding in this species is apparently limited to albumin and CBG.

Androgen-Binding Protein↗
PubMed1986

Purification and characterization of the reconstitutively active phosphate transporter from rat liver mitochondria.

Procedures have been developed for the purification of a nearly homogeneous, highly active phosphate transport system from rat liver mitochondria in either a two-subunit (alpha, beta) or a single subunit (beta) form. Significantly, both forms display a similar high magnitude N-ethylmaleimide (NEM)-sensitive Pi/Pi exchange activity upon incorporation into phospholipid vesicles. The transport system is extracted from hypotonically shocked mitoplasts with Triton X-114 and purified in the presence of cardiolipin by sequential chromatography on hydroxylapatite, DEAE-Sepharose CL-6B, and Affi-Gel 501. Depending on the conditions used to elute the transporter from Affi-Gel 501, preparations are obtained which, when analyzed by high resolution sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis, consist of either a single 33-kDa protein (beta) or a 33-kDa (beta) plus a 35-kDa (alpha) component. In preparations yielding the latter result, both bands display a nearly equivalent Coomassie staining intensity. Furthermore, after alkylation with NEM, the two protein bands co-migrate. Fluorography indicates that the coalesced band contains [3H]NEM. Upon reconstitution of the purified Pi carrier into liposomes, direct measurement of both the initial transport rate and the amount of protein that actually incorporates into the phospholipid vesicles yields a specific transport activity of 22.6 mumol/min/mg of protein. The exchange is characterized by a first order rate constant of 0.85 min-1, a t1/2 of 49 s, and is inhibited by sulfhydryl reagents (i.e., NEM, p-chloromercuribenzoate, and mersalyl). It is also substantially inhibited by diethyl pyrocarbonate, N-acetylimidazole, phenylglyoxal, and 5-dimethylaminoaphthalene-1-sulfonyl chloride. In addition to providing a simple, rapid method for preparing the NEM-sensitive phosphate carrier in nearly homogeneous form, these studies provide new information about the catalytically active species of the carrier, its kinetic properties, and its inhibitor sensitivities.

Animals↗
PubMed1985

Control of plasma sex steroid-binding protein (SBP) in the little brown bat: effects of thyroidectomy and treatment with L- and D-thyroxine on the induction of SBP in adult males.

The male little brown bat is a seasonally reproductive mammal that exhibits dramatic increases in plasma concentrations of sex steroid-binding protein (SBP) in the spring, following arousal from hibernation. Adult male bats, aroused prematurely from hibernation, were found to exhibit increases in plasma SBP titers that were comparable to those observed during normal spring arousal. To evaluate the role of the thyroid gland in the control of SBP in this species, plasma SBP concentrations were determined at weekly intervals in adult male bats that were either thyroparathyroidectomized (TRX) or sham operated (SHAM) after arousal from hibernation. Plasma SBP titers in SHAM males increased markedly within the first week after arousal and by 3 wk had reached levels 20-fold higher than those measured in hibernating controls. In contrast, plasma SBP values in the TRX animals did not increase significantly following arousal but were maintained at low basal levels throughout the experiment. The postarousal rise in SBP, which was blocked by TRX, was completely restored by implantation of either L- or D-thyroxine pellets. In male bats, TRX also hindered the normal postarousal atrophy of the sex accessory glands and resulted in attenuation of the postarousal increases in plasma testosterone concentrations. These effects of TRX were also prevented by treatment with thyroxine. Thus, the thyroid appears to play a significant role in the control of the postarousal rise of SBP in the little brown bat and may be an important factor in the regulation of reproductive function in this species.

Animals↗
PubMed1984

Thyroid hormone. Aldosterone antagonism in cultured epithelial cells.

Thyroid hormone (T3) has been demonstrated to inhibit the action of aldosterone on sodium transport in toad urinary bladder and rat kidney. We have examined the effect of T3 on aldosterone action and specific nuclear binding in cultured epithelial cells derived from toad urinary bladder. In cell line TB6-C, addition of 5 X 10(-8) M T3 to culture media for up to 3 days results in no change in short-circuit current or transepithelial resistance. This concentration of T3 completely inhibits the maximal increase in short-circuit current in response to 1 X 10(-7) M aldosterone. The inhibition can be demonstrated with 18 h preincubation or with simultaneous addition of T3 and aldosterone. The half-maximal concentration for the inhibition of the aldosterone effect is approx. 5 X 10(-9) M T3. T3 has no effect on cyclic AMP-stimulated short-circuit current in these cells. The effect of T3 on nuclear binding of [3H]aldosterone was examined using a filtration assay with data analysis by at least-squares curve-fitting program. Best fit was obtained with a model for two binding sites. The dissociation constants for the binding were K'd1 = (0.82 +/- 0.36) X 10(-10) M and K'd2 = (3.2 +/- 0.60) X 10(-8) M. The half-maximal concentration for aldosterone-stimulated sodium transport in these cells is approx. 1 X 10(-8) M. Analysis of nuclear aldosterone binding in cells preincubated for 18 h with 5 X 10(-8) M T3 showed a K'd1 = (0.15 +/- 0.10) X 10(-10) M and K'd2 = (3.5 +/- 0.10) X 10(-8) M. We conclude that T3 inhibits the action of aldosterone on sodium transport at a site after receptor binding in the nucleus.

Aldosterone↗
PubMed1984

An outbreak of influenza a in the highlands of Papua New Guinea.

In December 1982 and the early months of 1983, there was increased reporting of influenza-like illness from hospitals and health centres across the highlands region of Papua New Guinea. During this period, which fell in the highland wet season, influenza A viruses were isolated in routine surveillance specimens from a population of monitored children in the Goroka area in the Eastern Highlands. Influenza A viruses were also isolated in the investigation of a nearby rural outbreak of influenza-like illness. Samples of viruses isolated in these investigations were serotyped as most resembling the A/Philippines/2/82 strain. The contribution of these findings to the epidemiology of influenza in tropical countries, the role of influenza in the pathogenesis of pneumonia and possible interactions with bacteria and porcine influenza strains was discussed.

Adult↗
PubMed1983

Treatment of intracranial dengue virus infections in mice with a lipophilic derivative of ribavirin.

Rimantadine, ribavirin, and 6-mercapto-9-(tetrahydro-2-furyl)purine, administered intraperitoneally every 8 h for 7 days starting minutes after virus challenge, had no effect on survival and mean survival time of BALB/c mice inoculated intracranially with dengue virus type 2. In contrast, intraperitoneal treatment with ribavirin 2',3',5'-triacetate, a lipophilic analog of ribavirin, effected significant increases in both mean survival time and survival rate, suggesting that ribavirin 2',3',5'-triacetate may be superior to rabavirin for treatment of viral diseases of the brain.

Adamantane↗