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Biomedical subjects

J W Porter

Publications and source records attributed to J W Porter.

At least 19 recordsLinked to original sources
PubMed2002

Impacts of water management options on flows in the Condamine River in Southern Queensland.

This paper examines the implications for river flows of a number of water practices and potential management options in the alluvial plains of the Upper Condamine River. It is an intensively cultivated area where irrigation is limited by the availability of water resources. The practice of capturing overland flows was investigated by the development of a model that simulates the performance of clusters of offstream storages up to sub-catchment scale. Management options examined included improvement to on-farm water use efficiency, the suppression of evaporation from open water storages, increasing the depth of those storages, decreasing their number, and improved tailwater return from irrigated land. Impacts of management options were analysed using a catchment scale water allocation model.

Agriculture↗
PubMed1999

Emerging marine diseases--climate links and anthropogenic factors.

Mass mortalities due to disease outbreaks have recently affected major taxa in the oceans. For closely monitored groups like corals and marine mammals, reports of the frequency of epidemics and the number of new diseases have increased recently. A dramatic global increase in the severity of coral bleaching in 1997-98 is coincident with high El Niño temperatures. Such climate-mediated, physiological stresses may compromise host resistance and increase frequency of opportunistic diseases. Where documented, new diseases typically have emerged through host or range shifts of known pathogens. Both climate and human activities may have also accelerated global transport of species, bringing together pathogens and previously unexposed host populations.

Animals↗
PubMed1989

Bleaching in reef corals: Physiological and stable isotopic responses.

During the late summer to fall of 1987, Caribbean reef corals experienced an intense and widespread discoloration event described as bleaching. Contrary to initial predictions, most bleached corals did not die. However, energy input from zooxanthellae decreased, as estimated from: (i) delta(13)C values, a measure of the discrimination against (13)C in (12)C/(13)C assimilation, of skeletal aragonite; (ii) in situ photosynthesis-irradiance measurements; (iii) and tissue biomass parameters of Montastraea annularis and Agaricia lamarcki. The delta(18)O signal, a measure of the discrimination against (18)O in (16)O/(18)O assimilation, from M. annularis skeletons demonstrated that this event coincided with abnormally elevated water temperatures.

Journal Article↗
PubMed1986

Comparative atherogenic effects of cholesterol and cholesterol oxides.

Previous findings indicating that the oxidation products of cholesterol are associated with atherogenicity have led to a comparative study of the subchronic effects of feeding rabbits purified cholesterol, oxidized cholesterols free of cholesterol and cholesterol esters, or a mixture of cholesterol and oxidized cholesterols. Macroscopically, the cholesterol-fed animals exhibited 6-fold more arterial lesions than the animals fed cholesterol-free oxidized cholesterols. Microscopically, there was no statistically significant difference from the control in the number of histochemically-defined lesions in any of the groups. However, the lesions in the cholesterol-fed group were more severe, as indicated by a statistically significant increase in the magnitude of the lesions. This increased severity was also characterized by greater frequency and intensity of Azure A/Thionin, VonKossa, and Horseradish Peroxidase-Wheat Germ Agglutinin staining. Electron-microscopic studies of normal appearing arterial tissues showed an increased density of viable smooth muscle cells and an increase in vacuolar extracellular debris in the cholesterol-fed group. Oxidized cholesterols in the concentrations and relative compositions administered here are markedly less atherogenic to rabbits than highly purified cholesterol.

Animals↗
PubMed1985

Mechanism of glucagon inhibition of liver acetyl-CoA carboxylase. Interrelationship of the effects of phosphorylation, polymer-protomer transition, and citrate on enzyme activity.

The short-term regulation of rat liver acetyl-CoA carboxylase by glucagon has been studied in hepatocytes from rats that had been fasted and refed a fat-free diet. Glucagon inhibition of the activity of this enzyme can be accounted for by a direct correlation between phosphorylation, polymer-protomer ratio, and activity. Glucagon rapidly inactivates acetyl-CoA carboxylase with an accompanying 4-fold increase in the phosphorylation of the enzyme and 3-fold increase in the protomer-polymer ratio of enzyme protein. Citrate, an allosteric activator of acetyl-CoA carboxylase required for enzyme activity, has no effect on these phenomena, indicating a mechanism that is independent of citrate concentration within the cell. The observation of these effects of glucagon on acetyl-CoA carboxylase activity is absolutely dependent upon the minimization of proteolytic degradation of the enzyme after cell lysis. Therefore, for the first time, an interrelationship has been demonstrated between phosphorylation, protomer-polymer ratio, and citrate for the inactivation of acetyl-CoA carboxylase by glucagon.

Acetyl-CoA Carboxylase↗
PubMed1985

Purification of nucleotide-requiring enzymes by immunoaffinity chromatography.

Monospecific (affinity-purified) anti-(yeast glucose-6-phosphate dehydrogenase) IgG inhibits three different NADPH-requiring enzymes, chicken liver dihydrofolate reductase, pigeon liver fatty acid synthetase and chicken liver malic enzyme. The inhibition of all three enzymes was approx. 50% in a 2h incubation with 100 micrograms of IgG. Similarly, with several different NADH-requiring enzymes, an immunocrossreactivity was observed. Monospecific anti-(rabbit muscle glyceraldehyde-3-phosphate dehydrogenase) IgG inhibited yeast alcohol dehydrogenase and pig heart malate dehydrogenase by 39% and 55% respectively. The cross-reactivity observed was tested by affinity chromatography. Immunoaffinity columns made with each monospecific IgG were able to bind each of the enzymes it immunotitrated. Enzymes were eluted with a nondenaturing solvent with little loss of activity. The immunoaffinity column with monospecific anti-(glucose-6-phosphate dehydrogenase) IgG as the bound ligand was also used to purify partially (over 150-fold) both isocitrate dehydrogenase and dihydrofolate reductase from crude rat liver homogenate.

Animals↗
PubMed1985

Characterization of fatty acid synthetase cDNA clone and its mRNA.

Four cDNA clones have been identified by hybrid-select translation to contain the sequences complementary to fatty acid synthetase mRNA. The restriction mapping of these clones indicated that three of these, pFAS-7, pFAS-17 and pFAS-18, have sequences in common, and a fourth, pFAS-15, did not hybridize with the others, suggesting sequence to another region of the mRNA. Northern analysis of cytoplasmic poly(A) +RNA showed the presence of two bands at 9.2 Kb and 8.4 Kb. Similar analysis of nuclear RNA also showed the presence of two bands at 14 and 11 Kb. These probably represent unprocessed transcripts. Southern analysis of genomic DNA digested with EcoRI, BamHI, HindIII and PstI indicate the presence of a single gene copy for fatty acid synthetase.

Animals↗
PubMed1985

Isolation, purification, and characterization of a peptide that contains the beta-ketoacyl reductase, enoyl reductase, and beta-hydroxyacyl dehydrase activities of the pigeon liver fatty acid synthetase.

Controlled proteolytic cleavage of pigeon liver fatty acid synthetase with elastase (4% w/w) for 5 h yields two peptides that are designated II and IV. After 5 h of proteolysis the incubation mixture containing these peptides retains all of the component enzyme activities of the fatty acid synthetase complex. The two peptides are then separated by chromatography on an Affi-Gel Blue column. Gel filtration of the fraction containing peptide II yields a homogeneous peptide as shown by polyacrylamide gel electrophoresis in the presence and absence of sodium dodecyl sulfate. The molecular weight of this peptide has been estimated to be 130 000 by sodium dodecyl sulfate--polyacrylamide gel electrophoresis, size exclusion chromatography, and amino acid analysis. The sedimentation coefficient for peptide II is approximately 7.4S. Peptide II contains the domains for the beta-ketoacyl and enoyl reductases and beta-hydroxyacyl dehydrase activities of the fatty acid synthetase complex.

3-Oxoacyl-(Acyl-Carrier-Protein) Reductase↗
PubMed1984

Isopentenyl pyrophosphate isomerase and prenyltransferase from tomato fruit plastids.

Isopentenyl pyrophosphate isomerase has been isolated from an extract of tomato fruit plastids and purified 245-fold by fractionation with ammonium sulfate, gel filtration on Bio-Gel A 1.5m, ion-exchange chromatography on DEAE-cellulose, gel filtration on Sephadex G-100, and chromatofocusing. Gel filtration on Sephadex G-100 separated the isopentenyl pyrophosphate isomerase from a prenyltransferase fraction that catalyzed the conversion of isopentenyl pyrophosphate to acid-labile compounds in the presence of dimethylallyl, geranyl, or farnesyl pyrophosphates. The molecular weights of the isopentenyl pyrophosphate isomerase and prenyltransferase were determined to be 34,000 and 64,000, respectively, by gel filtration on Sephadex G-100. The only cofactor required by either the isomerase or the prenyltransferase was a divalent cation, either Mg2+ or Mn2+. Isopentenyl pyrophosphate isomerase could also be totally inactivated by 1 X 10(-3) M iodoacetamide, and this property was utilized in the assay of prenyltransferase activity in the presence of contaminating isomerase. The inactivation of isomerase by iodoacetamide is consistent with the stabilization of isopentenyl pyrophosphate isomerase by dithiothreitol. The Km of isopentenyl pyrophosphate isomerase for isopentenyl pyrophosphate was found to be 5.7 X 10(-6).

Carbon-Carbon Double Bond Isomerases↗
PubMed1984

Cloning of DNA complementary to rat liver fatty acid synthetase mRNA.

Clones, containing DNA complementary (cDNA) to rat liver fatty acid synthetase mRNA, were constructed and identified. cDNA of these clones was then used as a probe to quantify mRNA. The cDNA was synthesized to partially purified rat liver fatty acid synthetase mRNA. Double-stranded cDNA was then prepared and inserted into the PstI site of pBR322 using oligo(dG) X oligo(dC) tailing. Initial selection of the clones was by differential colony hybridization employing [32P]cDNA synthesized from poly(A)-rich mRNA, enriched and non-enriched in fatty acid synthetase mRNA, as probes. Plasmids, containing specific sequences complementary to the fatty acid synthetase mRNA, were identified by hybrid-arrest translation. Cloned cDNA inserts ranged from 300 to 1400 base pairs. Cloned cDNA was employed to probe for mRNA in hybridizations via the dot-blot method. These studies demonstrated an increase in fatty acid synthetase mRNA during dietary induction, which suggests that regulation may involve changes in transcription or changes in post-transcriptional processing of the mRNA.

Animals↗
PubMed1984

Antibody preference for the catalytically active form of beta-hydroxy-beta-methylglutaryl coenzyme A reductase.

The catalytically inactivating subset within rabbit serum polyclonal antibody to the solubilized, purified 55,000 to 60,000 dalton active fragment of rat liver microsomal beta-hydroxy-beta-methylglutaryl coenzyme A reductase immunoinactivates this enzyme with little or no diminution of effect by enzyme catalytically inactivated by incubation of microsomes with ATP,Mg++. Reactivation of inactive enzyme with ethanol-treated rat liver phosphatase restores antibody affinity showing that the catalytically inactivating subset of antibody exhibits marked or complete affinity for the active enzyme over the ATP,Mg++- inactivated form. This means that immunoinactivation using this antibody is not a valid way of measuring changes in the specific activity of the enzyme via phosphorylation-dephosphorylation. Preference for the active enzyme has not been obvious because when different amounts of enzyme activity are used in immunotitrations of samples of low activity, apparent differences in specific activity are observed when none actually exist. If precautions are not taken, results are obtained supporting phosphorylation by using an antibody that is not capable of distinguishing it.

Adenosine Triphosphate↗
PubMed1983

Fatty acid synthetase, malic enzyme and other NADP+ binding dehydrogenases have similar antigenic determinant(s) at the NADPH binding domain.

Rabbit IgG prepared against malic enzyme inhibits pigeon liver fatty acid synthetase activity. By screening a number of polyclonal antibodies raised to several dehydrogenases, we have discovered that there is a direct relationship between this cross-reactivity and the existence of a common structural domain whose function is the binding of NADP+/NADPH. The presence of NADP+/NADPH in small concentrations protects against this immunoinhibition, thereby indicating a competitive binding of nucleotide and site-specific antibody at the antigenic domain. These data provide further support for the existence of an antigenic domain in the NADPH binding region of dehydrogenases which is responsible for the production of NADPH site-specific antibodies in polyclonal antisera.

Animals↗
PubMed1983

Degradation of pigeon liver fatty acid synthetase in the absence of exogenous proteinases.

The homogeneity of pigeon liver fatty acid synthetase has been rigorously tested by physicochemical techniques and crossed-rocket immunoelectrophoresis. The enzyme has also been incubated for 1 h at 100 degrees C in 2% sodium dodecyl sulfate and 0.1 M dithiothreitol. The number of protein components on gel electrophoresis and of dansylated amino acids increased as a function of incubation time. Furthermore, the minor proteins observed after gel electrophoresis cross-reacted with antibody raised to the synthetase. Proteolysis was not chemically mediated by the detergent, the reducing agent or the buffer conditions chosen. Several commercially prepared proteins were not degraded by this procedure, and two proteins were recalcitrant to hydrolysis when included in the same incubation mixture as the synthetase. The inclusion of certain microbial proteinase inhibitors decreased the amount of degradation. This demonstrated that hydrolysis of the synthetase is mediated by a specific vertebrate enzyme which retains activity under denaturing conditions at 100 degrees C. Further degradation is also observed after individual treatment of four limited digestion products from the pigeon liver fatty acid synthetase, suggesting the possibility of an inherent proteolytic activity within the complex.

Animals↗
PubMed1983

Induction of fatty acid synthetase and acetyl-CoA carboxylase by isolated rat liver cells.

Current studies on the synthesis of long-chain fatty acids by isolated rat liver cells are largely concerned with the regulation of the activity of previously existing acetyl-CoA carboxylase and fatty acid synthetase, and with the regulation of the quantity of these enzymes. These studies have required the development of methods for obtaining high yields of viable hepatocytes that respond to hormonal treatment. Such methods have been developed over the past 10-15 years through the efforts of several laboratories. These studies have also required the development of a method to determine whether a change in the activity of an enzyme is due to a modification of preexisting enzyme or to a change in quantity of that enzyme. The most satisfactory method to use for such studies is immunotitration of enzyme activity. In recent years studies on the regulation of acetyl-CoA carboxylase have largely centered upon the effect of phosphorylation-dephosphorylation on the activity of this enzyme and whether glucagon inhibits the activity of this enzyme through this process. Much data from a number of laboratories have suggested that glucagon regulates the activity of this enzyme through phosphorylation-dephosphorylation. However, several of these studies involved the use of crude systems in which competing enzymes and substrates that can significantly interfere with acetyl-CoA carboxylase activity measurements were still present. Hence, a confirmation of these studies needs to be carried out under conditions in which the effects of competing enzymes and substrates are eliminated. Studies on changes in quantity of acetyl-CoA carboxylase and fatty acid synthetase have shown that these enzymes are induced by the fasting and refeeding of animals. They have also shown that insulin stimulates (10- to 30-fold) the induction of these enzymes. This induction appears to be due to a change in the quantity of translatable mRNA which may, in turn, be due to a change in the rate of transcription of the genes coding for these enzymes.

Acetyl-CoA Carboxylase↗
PubMed1983

Antibodies specific for NADPH-binding region of enzymes possessing dehydrogenase activities.

The results reported in this paper show the presence of a population of antibodies in rabbit polyclonal antiserum that recognize an antigenic site at the NADPH-binding region of enzymes possessing dehydrogenase activities. Antisera from rabbits immunized with glucose-6-phosphate dehydrogenase or fatty acid synthetase were found to inactivate the enzyme dihydrofolate reductase. The inhibitory effect of this site-specific antibody is a time- and concentration-dependent reaction. This immunoinactivation is prevented by preincubation of the enzyme with NADPH.

Animals↗