Biomedical subjects

J A Sharp

Publications and source records attributed to J A Sharp.

35 records · Page 2Linked to original sources

PubMed1983

The effects of Al3+, Cd2+ and Mn2+ on human erythrocyte choline transport.

The effects of Al3+, Cd2+ and Mn2+ on human erythrocyte choline transport, Na-K-ATPase, Ca-Mg-ATPase and intracellular K+ levels were examined. The concentrations used were below the levels which caused significant haemolysis (less than or equal to 300 microM). All three cations inhibited concentrative choline accumulation over 3 hr [IC50 values at 1 microM choline were 35 microM (AlCl3), 250 microM (CdCl2) and 300 microM (MnCl2)] but at the concentrations tested, none decreased initial rates of choline uptake. The effects of Cd2+ and Mn2+ (but not Al3+) on choline accumulation were reversed by removing the cations from the extracellular medium by washing. All three cations also inhibited efflux of choline, at 1 microM choline, 30% inhibition being produced by 33 microM AlCl3, 81 microM CdCl2 and 111 microM MnCl2. At subhaemolytic concentrations, only CdCl2 inhibited Na-K-ATPase, (IC50 = 147 microM) and none of the cations significantly inhibited Ca-Mg-ATPase. Intracellular K+ levels were only reduced by the highest concentration of AlCl3 used (100 microM). These results suggest that inhibition of choline accumulation and efflux in erythrocytes by Al3+, Cd2+ and Mn2+ is not explicable solely in terms of either inhibition of Ca-Mg-ATPase, or inhibition of Na-K-ATPase causing reduced intracellular K+. Our conclusions are similar to those previously obtained using synaptosomes and provide support for the hypothesis that inhibition of choline transport by Al3+ may contribute to a number of disease states.

Aluminum↗

PubMed1983

Initial-velocity kinetics of succinoyl-coenzyme A-3-oxo acid coenzyme A-transferase from sheep kidney.

The initial-velocity kinetics of sheep kidney CoA-transferase are consistent with a Ping Pong mechanism. A KAcAc-CoA of 2.7 X 10(-5) M, KSucc-CoA of 1.6 X 10(-4) M, KSucc of 5.6 X 10(-3) M and KAcAc of 6.7 X 10(-5) M were determined by using a direct assay system that monitors the concentration of magnesium acetoacetyl-CoA enolate. However, product-inhibition kinetics of sheep kidney CoA-transferase are inconsistent with a Ping Pong mechanism. The possible involvement of separate binding sites for succinate and acetoacetate are discussed.

Acetoacetates↗

PubMed1983

A kinetic mechanism for the poly(C)-dependent ATPase of the Escherichia coli transcription termination protein, rho.

A study of the initial velocity kinetics of the Escherichia coli transcription termination protein rho, with respect to its poly(C)-dependent ATPase, indicates that this reaction occurs by an ordered sequential mechanism. Product inhibition and substrate analogue studies suggest that ATP binding must precede the binding of poly(C) and that the order of release of the products is ADP followed by Pi, then poly(C). A possible mechanism for relating the ATPase to the termination reaction of rho is discussed in relation to the model for rho proposed by Richardson (5).

Adenosine Diphosphate↗

PubMed1983

Transcription of herpes simplex virus genes in vivo: overlap of a late promoter with the 3' end of the early thymidine kinase gene.

We identified in herpes simplex virus type 1-infected cells six cytoplasmic transcripts which were complementary to BamHI restriction endonuclease fragment Q. Two transcripts appeared in major amounts compared with the other four. One major transcript of about 1.4 kilobases was the mRNA for the viral thymidine kinase, was synthesized at intermediate times, and was classified as a beta transcript. The other major transcript was synthesized at late times and was classified as a gamma transcript. This late transcript was about 3 kilonucleotides long and was transcribed in the same direction as the gene for thymidine kinase. The 5' end of this late RNA was located by RNA sequence analysis and was 23 nucleotides downstream from the polyadenylation site for the thymidine kinase mRNA. This finding led to the conclusion that the control region for the 3-kilobase gamma transcript is contained within the 3' untranslated region of the thymidine kinase transcript.

Base Sequence↗

PubMed1983

Pausing and termination of human RNA polymerase II transcription at a procaryotic terminator.

Kinetic analyses of runoff transcription in a cell-free eucaryotic transcription system revealed that the bacteriophage lambda 4S RNA terminator caused human RNA polymerase II to pause on the template and partially terminate transcription of transcripts initiated by the adenovirus 2 major late promoter. Analogous to the procaryotic RNA polymerase, the eucaryotic enzyme terminated just beyond the guanine-plus-cytosine-rich region of dyad symmetry in the terminator sequence. These results suggest that the eucaryotic RNA polymerase II may respond to transcription termination sequences similar to those used by the procaryotic enzyme. However, similar templates containing lambda tint or lambda tR1 terminators did not elicit pausing or termination, suggesting that other features, such as sequence specificity, may also be involved.

Bacteriophage lambda↗

PubMed1981

Nucleotide sequence of the thymidine kinase gene of herpes simplex virus type 1.

We have determined the complete nucleotide sequence of the thymidine kinase (ATP:thymidine 5' phosphotransferase, EC 2.7.1.21) gene of herpes simplex virus type 1 strain CL101 from a plasmid clone of viral DNA derived by Enquist et al. [Enquist, L. W., Vande Woude, G. F., Wagner, M., Smiley, J. R. & Summers, W. C. (1979) Gene 7, 335-342]. A cDNA copy of the 5' end of thymidine kinase mRNA was also analyzed to locate the transcribed sequences. The transcribed portion of the gene is approximately 1300 nucleotides in length and appears to contain no intervening sequences. There is an untranslated region of 107 nucleotides at the 5' end of the mRNA followed by an open reading frame of 1128 nucleotides. The gene is thus capable of coding for a protein of 376 amino acids. Sequences similar to those thought to be involved in control of transcription and translation of a variety of eukaryotic and viral genes such as a "Hogness box" and A-A-T-A-A-A polyadenylylation signals are also present in the herpesvirus thymidine kinase gene.

Amino Acid Sequence↗

PubMed1978

Purification and properties of succinyl-coenzyme A-3-oxo acid coenzyme A-transferase from sheep kidney.

CoA-transferase (succinyl-CoA-3-oxo acid CoA-transferase, EC 2.8.3.5) isolated from sheep kidney was purified to homogeneity. The purified enzyme has a specific activity of approx. 200 units/mg. A mol.wt. of 110000 was obtained by gel filtration on Sephadex G-200, and a lower mol.wt. of 102000 was determined by analytical ultracentrifugation. A sedimentation coefficient of 5.6S was also determined. A subunit mol.wt. of 56000 was obtained by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Isoelectric focusing of sheep kidney extracts indicated the presence of a single band of CoA-transferase activity with pI9.0. However, isoelectric focusing of purified CoA-transferase showed the presence of two peaks of CoA-transferase activity with pI values of 8.7 and 8.4, suggesting the presence of proteolytic activity during purification. Evidence for sheep kidney CoA-transferase being a dimer of two identical subunits has been obtained from sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, the amino acid composition, peptide 'mapping' and N-terminal analysis.

Acetoacetates↗

PubMed1975