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Biomedical subjects

D Brown

Publications and source records attributed to D Brown.

At least 685 records · Page 38Linked to original sources
PubMed1991

Bcy1, the regulatory subunit of cAMP-dependent protein kinase in yeast, is differentially modified in response to the physiological status of the cell.

The regulatory subunit of cAMP-dependent protein kinase in yeast, encoded by the BCY1 gene, is known to be required under certain conditions such as growth on nonfermentable carbon sources and entry into stationary phase. We have identified novel isoforms of Bcy1 in cells under these conditions. The isoforms are distinguishable by their migration on one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and 2-dimensional nonequilibrium pH gradient gel electrophoresis. The isoforms observed by one-dimensional SDS-PAGE bind cAMP, as determined by [32P]8-azido-cAMP labeling (diagnostic of Bcy1 protein). Proteins isolated from cells grown to stationary phase in rich medium exhibit five antibody-reactive bands, by one-dimensional SDS-PAGE immunoblot analysis, with apparent molecular masses of 50, 52, 55, 59 and 61 kDa. Total Bcy1 protein increases at least 8-fold between exponential and stationary phase. Analysis of proteins from a variety of yeast mutants indicated that 1) many of the observed modifications of Bcy1 are dependent upon the presence of the Ser-145 phosphorylation site; 2) the appearance of the 59- and 61-kDa bands is dependent upon the presence of Yak1 kinase; and 3) Bcy1 protein is modified even in the absence of cAMP-dependent protein kinase catalytic subunits. Cells carrying the bcy1(ala145) allele exhibit non-wild type growth, indicating that these modifications may be functionally significant.

Blotting, Western↗
PubMed1991

Lipid peroxidation in electroporated hepatocytes occurs much more readily than does hydroxyl-radical formation.

1. Rat hepatocytes suspended in 0.25 M-sucrose were electropermeabilized. This completely disrupted their plasma-membrane permeability barrier. 2. The endoplasmic reticulum in electroporated hepatocytes appeared morphologically preserved and maintained its permeability barrier as evidenced by electron-microscopic examination and latency measurements on luminal reticular enzymes. 3. Upon aerobic incubation with an NADPH-generating system and iron/ADP, porated hepatocytes peroxidized their membrane lipids at rates similar to those of matched microsomal preparations. 4. When hepatocytes were incubated with iron/EDTA and azide, radical formation detectable with dimethyl sulphoxide (DMSO) was only 10-20% that shown by microsomes. Omitting azide abolished hepatocyte reactivity with DMSO completely. Effects of hydroxyl-radical (.OH) scavengers and of added catalase suggest that the radical detected by DMSO is .OH. 5. Cytosolic inhibitor(s) from hepatocytes seemed to be a major factor limiting .OH formation. These were macromolecular, but showed a degree of heat-stability. Dialysis largely abolished inhibition, but this could be restored again by adding GSH. 6. Since .OH formation in hepatocytes seems to be much more stringently prevented than lipid peroxidation, free-radical damage originating from intracellular redox systems seems more likely to take the form of lipid peroxidation.

Animals↗
PubMed1991

Characterization of the major matrix degrading metalloproteinase of human corneal stroma. Evidence for an enzyme/inhibitor complex.

The human cornea is an avascular, highly organized tissue with the unique property of transparency. While the extracellular matrices of this tissue are composed of a variety of collagen types, proteoglycans and glycoproteins, little is known of the normal degradation and remodeling of these components. We examined the capacity of organ cultured human ocular tissues to produce and secrete metalloproteinases, a family of related enzymes capable of digesting a variety of extracellular matrices. We demonstrated that while enzymatic activities similar to type I collagenase and stromelysin are produced, the predominant activities of the corneal stroma and keratocyte cultures are a 68-kDa gelatinase. In our hands, this enzyme does not appear to be induced significantly by phorbol esters in vitro. In addition, this enzyme appears to be secreted as a complex with a 21-kDa protein that functions as an enzymatic inhibitor. Moreover, the keratocytes also produce a 28-kDa inhibitor which has similar properties to tissue inhibitor of metalloproteinase (TIMP).

Adult↗
PubMed1991

Effectiveness of a purified human hemoglobin as a blood substitute in the perfused rat liver.

The efficacy of purified cross-linked human hemoglobin solution in maintaining the metabolic integrity of perfused livers from fed rats was determined and compared with that of livers recirculated with red blood cells, perfluorocarbon, and Krebs' Ringer bicarbonate buffer media at normal and accelerated flow rates. The data indicate that oxygen utilization was comparable in livers perfused with red blood cell medium (53.5 +/- 4.0 microL.g liver-1.min-1), hemoglobin (45.7 +/- 1.9), and perfluorocarbon (57.2 +/- 6.1) and less in livers perfused with Krebs' Ringer bicarbonate buffer solution at normal (17.4 +/- 1.4) and high (27.7 +/- 1.4) flow rates. Bile flow, the outflow of glucose and lactic acid, and residual glycogen levels were similar when livers were perfused with red blood cells (hematocrit, 19) and hemoglobin solutions containing 7 g hemoglobin/dL at flow rates of 1.1-1.2 mL.g liver-1.min-1. However, livers perfused with perfluorocarbon at 1.1 mL.g-1.min-1 showed a significantly greater (P less than 0.01) decline in bile flow and outflow of glucose and lactic acid. Livers perfused with Krebs' Ringer bicarbonate buffer at normal (1.3 mL.g-1.min-1) and accelerated flow rates (3.0 mL.g-1.min-1) also showed a progressive decrease in bile flow and marked glycogenolysis as well as depletion of adenosine triphosphate content. In addition, morphological studies (light and electron microscopy) showed more vacuoles, membrane alterations, and increased mitochondrial swelling in livers perfused with Krebs' Ringer bicarbonate buffer and perfluorocarbon. These findings suggest that hepatocyte function in livers from fed rats is maintained equally well with hemoglobin solutions and with red blood cell medium, suggesting that cross-linked hemoglobin solution may serve as an effective blood substitute for maintaining adequate oxygenation and metabolic integrity of the isolated perfused rat liver.

Analysis of Variance↗
PubMed1991

Translation of hepatitis A virus RNA in vitro: aberrant internal initiations influenced by 5' noncoding region.

Hepatitis A virus (HAV) RNAs were translated in vitro in rabbit reticulocyte lysates. The pattern of proteins synthesized from full-length HAV RNA was highly complex, consisting of a continuous spectrum of polypeptides ranging from less than 20,000 to greater than 200,000 Da. The pattern was not significantly altered by varying incubation times, ion, or other reaction parameters, or by the addition of HeLa or BS-C-1 cell extracts to the translation reactions. Plasmids engineered with mutations in the 3C coding region produced transcripts which directed the synthesis of the same overall pattern of polypeptide products as those transcribed from wild-type sequences, suggesting that protein processing by 3C did not generate the complex set of protein products. Translation of RNA containing only the P3 coding region of HAV, directly adjacent to the HAV 5' noncoding region, generated a set of protein products which precisely matched a subset of those synthesized from full-length HAV RNA. The translation products of P3 RNA, full-length RNA, and mutant 3C-containing RNAs were analyzed by immunoprecipitation with antisera specific for 3D, VP1, and 2C sequences; several products were subjected to N-terminal sequence analysis. All together, the results demonstrate that translation of HAV RNA in rabbit reticulocyte lysates initiates predominantly at a large number of internal AUG codons, especially those in the P3 coding region. A minor population of products is initiated from sites in the P1 and P2 regions. The latter proteins undergo some proteolytic processing, at unidentified sites, catalyzed by 3C protein sequences. Replacement of the HAV 5' noncoding region with encephalomyocarditis virus 5' end sequences increased initiation at the correct polyprotein start site and both reduced and altered the products generated by internal initiation.

3C Viral Proteases↗