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G G Johnson

Publications and source records attributed to G G Johnson.

30 records · Page 2Linked to original sources
PubMed1983

Isolation and characterization of a full-length expressible cDNA for human hypoxanthine phosphoribosyl transferase.

We have cloned a full-length 1.6-kilobase cDNA of a human mRNA coding for hypoxanthine phosphoribosyltransferase (HPRT; IMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) into a simian virus 40-based expression vector and have determined its full nucleotide sequence. The inferred amino acid sequence agrees with a partial amino acid sequence determined for authentic human HPRT protein. Transfection of HPRT-deficient mouse LA9 cells with the purified plasmid leads to the expression of human HPRT enzyme activity in cells stably transfected and selected for enzyme activity in hypoxanthine/aminopterin/thymidine medium.

Amino Acid Sequence↗
PubMed1982

Hypoxanthine-guanine phosphoribosyltransferase in human erythroid cells: posttranslational modification.

Hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8) (HGPRT) of human red blood cells has been separated into three major isoenzymes, the relative quantities of which change as the cell ages. The predominant isoenzyme in the youngest circulating red blood cells, reticulocytes, has the same isoelectric point as the single enzyme of lymphoblasts. This lymphoblast-like enzyme is diminished in older red cells, and the major fraction of HGPRT activity is recovered in the two more acidic isoenzymes. The HGPRT enzymes of human lymphoblasts and red cells have been purified to apparent homogeneity, as evidenced by the criterion of subunit molecular weight in NaDodSO4 gels. The lymphoblast enzyme dissociates to a single subunit (alpha) upon isoelectric focusing in 8 M urea and is presumed to be a homo dimer (alpha alpha). The red cell isoenzymes dissociate to two subunits, one with the same isoelectric point as that in lymphoblasts (alpha) and one more negatively charged (alpha'). We infer that the three major red cell isoenzymes, I-III, correspond to enzyme species with none (alpha alpha), one (alpha alpha'), or both (alpha' alpha') subunits modified. Tryptic peptide maps of these iodo[2-14C]acetamide-labeled enzyme subunits indicate that the one red cell subunit (alpha) is identical with that in lymphoblasts and that the second subunit (alpha') differs from these in only one of the five cysteine-containing tryptic peptides. These results indicate that the HGPRT subunit is subject to at least one covalent and site-specific modification in human erythroid cells.

Erythrocyte Aging↗
PubMed1980

Canine tuberculosis.

In a survey of 15,272 canine necropsies, natural infection with Mycobacterium tuberculosis was found to have been diagnosed in eight dogs (0.05%). Clinical findings were anorexia, loss of body weight, lethargy, vomiting, and leukocytosis; radiography revealed pleural and pericardial effusion, ascites, and hepatomegaly. Granulomatous lesions with acid-fast bacilli were consistently found. Mycobacterium tuberculosis was isolated from lesions in the lungs, liver, or lymph nodes of five dogs. All eight dogs had a history of contact with human patients with tuberculosis.

Animals↗
PubMed1979

Human and mouse hypoxanthine-guanine phosphoribosyltransferase: dimers and tetramers.

Human and mouse hypoxanthine-guanine phosphoribosyltransferase subunits combine to form an active heteropolymer. Dimers form the basic subunit structure of the enzymes, yet the dimers can readily associate to form tetramers. The equilibrium between dimers and tetramers is significantly influenced by the ionic strength of the enzyme solvent.

Animals↗
PubMed1977

Specificity of the weak binding between the phage SPO1 transcription-inhibitory protein, TF1, and SPO1 DNA.

The interaction of the phage SPO1 protein transcription factor 1 (TF1), with DNA has been analyzed by membrane filter binding and by sedimentation methods. Substantially specific binding of TF1 to helical SPO1 DNA can be demonstrated by nitrocellulose filter-binding assays at relatively low ionic strength (0.08). However, TF1-DNA complexes dissociate and reequilibrate relatively rapidly and this makes filter-binding assays unsuitable for quantitative measurements of binding equilibra. Accordingly, the sedimentation properties of TF1-DNA complexes have been explored and a short-column centrifugation assay has been elaborated for quantitative measurements. Preferential binding of TF1 to the hydroxymethyluracil-containing SPO1 DNA has also been demonstrated by short-column centrifugation. TF1 binds relatively weakly and somewhat cooperatively to SPO1 DNA at many sites; TF1-DNA complexes dissociate and reequilibrate rapidly. At 20 degrees C in 0.01 M phosphate, pH 7.5, 0.15 KC1, one molecule of TF1 can bind to approximately every 60 nucleotide pairs of SPO1 DNA.

Bacillus subtilis↗
PubMed1975

Bacteriophage SPO1 DNA- and RNA-directed protein synthesis in vitro: the effect of TF1, a template-selective transcription inhibitor.

Transcription factor one (TF1), a protein synthesized after infection of B. subtilis by phage SPO1, is a specific inhibitor of SPO1 in vitro transcription. In this paper, we investigate the effect of TF1 on SPO1-specific in vitro protein synthesis, using SPO1 DNA or messenger RNA as templates. Protein syhthesis is measured by incorporation of radioactive amino acids into acid insoluble form, synthesis of a phage-specific enzymatic activity, and analysis of radioactive polypeptides by acrylamide gel electrophoresis. TF1 is shown to inhibit the DNA-dependent synthesis of all SPO1 proteins which can be made in vitro, but to have no specific effect on RNA-dependent protein synthesis in vitro.

Bacillus subtilis↗
PubMedDate not supplied

Ibuprofen protects platelet cyclooxygenase from irreversible inhibition by aspirin.

Previous investigations have shown that ibuprofen inhibits the second wave of platelet aggregation and blocks the conversion of 14C-arachidonic acid to thromboxane. However, the influence of the drug on platelet function and cyclooxygenase is transitory, lasting only 24 hours. The present study has taken advantage of the short-lived influence of ibuprofen to study its interaction with the long-term effects of aspirin. As expected, both aspirin and ibuprofen suppressed platelet cyclooxygenase activity and function, but addition of aspirin to ibuprofen-treated platelets did not increase the degree of inhibition in vitro. Platelet function and prostaglandin synthesis recovered completely 26 hours following ingestion of ibuprofen, but remained compromised 26 hours after taking aspirin. When 650 mg of aspirin was administered after ibuprofen, platelet function and cyclooxygenase activity recovered as completely at 26 hours as did platelets which had been exposed to ibuprofen alone. Thus, prior exposure to ibuprofen in vivo completely protected cyclooxygenase from the irreversible effects of aspirin. Our findings indicate that ibuprofen-like indomethacin and other nonsteroidal antiinflammatory drugs react with the heme group of cyclooxygenase to prevent arachidonic acid conversion. Since ibuprofen completely blocks the effects of aspirin in platelets in vitro and in vivo, aspirin's primary influence on inhibition of cyclooxygenase must also be through action on the heme portion of the enzyme, rather than acetylation of the protein.

Animals↗