The Journal of biological chemistry
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The formation of bile pigment from heme by a reconstituted heme oxygenase system containing purified bovine spleen heme oxygenase, NADPH-cytochrome P-450 reductase, and biliverdin reductase was studied under an atmosphere containing 18,18O2. The product, bilirubin, was isolated and subjected to mass spectrometry, which revealed incorporation of 18O consistent with a two-molecule mechanism, whereby the product bile pigment contains oxygen atoms derived from two different oxygen molecules.
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Chronic metabolic acidosis increased the Na+-H+ exchange activity in isolated renal brush-border membrane vesicles. Treatment altered the initial rate of Na+ uptake by increasing Vm (acidotic, 15.3 +/- 0.7 nmol of Na+ X mg-1 X 2 s-1; normal, 11.3 +/- 0.9 nmol of Na+ X mg-1 X 2 s-1), and not the apparent affinity KNa+ (acidotic, 10.2 +/- 0.5 mM; normal 10.2 +/- 0.6 mM). Metabolic acidosis resulted in the proportional increase in 1 mM Na+ uptake at every intravesicular pH measured. ⋯ When the data were analyzed by the Hill equation, it was found that metabolic acidosis did not change the n (acidotic, 1.33 +/- 0.13; normal, 1.43 +/- 0.07) or the K'H+ (acidotic, 0.27 +/- 0.05 microM; normal, 0.28 +/- 0.06 microM), but increased the apparent Vm (acidotic, 1.10 +/- 0.08 nmol of Na+ X mg-1 X 2 s-1; normal, 0.81 +/- 0.07 nmol of Na+ X mg-1 X 2 s-1). The uptake of Na+ in exchange for H+ in membrane vesicles from normal and acidotic animals was not influenced by membrane potential. We conclude that metabolic acidosis leads to either an increase in the number of functioning exchangers or an increase in the turnover rate of the limiting step in the exchange.
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The addition of a purified mitochondrial pyridine nucleotide transhydrogenase enzyme preparation to complex I (NADH-CoQ reductase) results in a significant increase in the NADPH-AcPyAD+ transhydrogenase activity of the complex without influencing the NADH-AcPyAD+ transhydrogenase activity. When subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence of complex I, the purified transhydrogenase enzyme preparation was found to co-migrate with the Mr = 130,000 (130K) subunit of the NADH-CoQ reductase. Loss of the NADPH-NAD+ transhydrogenase activity of complex I following limited tryptic digestion was associated with a corresponding loss of the 130K subunit from the complex. ⋯ In this interpretation, an ordered binding of substrate involves an initial NADP(H) (or NADP+ photoprobe) interaction with a hydrophobic region at the transhydrogenation site. This initial reactivity is followed by a positioning of NAD(H) (or the NAD+ photoprobe analogue) above or periphery to the NADP(H) nucleotide present at the active site region. Supportive evidence for this model for transhydrogenation is presented and discussed.
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The general histidine-containing phosphocarrier protein (HPr) of the Salmonella phosphotransferase system is required for the phosphorylation of all sugar substrates by this system. The complete amino acid sequence of HPr, consisting of 84 amino acid residues, has been established. The sequence was determined by cleaving the protein with cyanogen bromide, trypsin, and with a protease from Staphylococcus aureus, followed by isolation and amino acid sequence determination of the resulting peptides. ⋯ In the present studies, three methods were used to predict the secondary structure of S. typhimurium HPr, the results were combined, and a secondary structure for the protein is proposed. Although the amino acid compositions and sequences of the S. typhimurium and S. aureus HPr proteins are quite different, 13 residues are identical in the sequence of the two proteins, and most of these are located near the active site histidine residue. In addition, the predicted secondary structures of the two proteins are quite similar; the additional 14 residues in S. typhimurium, located at the carboxyl terminal end, are predicted to form an alpha-helix.
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The amino acid sequence of bovine eye lens leucine aminopeptidase has been determined. Cyanogen bromide fragments, the COOH-terminal hydroxylamine fragment, and a large fragment obtained by digestion with Staphylococcus aureus protease were isolated from reduced and S-alkylated leucine aminopeptidase. The amino acid sequences of these fragments were determined by automated sequence analysis, by manual direct Edman degradation, and by the dansyl-Edman technique. ⋯ The polypeptide chain of leucine aminopeptidase comprises 478 residues, corresponding to a molecular weight of 51,691. No significant sequence homology with any other published protein primary structure could be detected. This is the first report of a complete amino acid sequence of an enzyme belonging to the class of two metal peptidases.