Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.7.1.4 (nitrite reductase)
 1,847 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The hemoprotein component of Salmonella typhimurium sulfite reductase (NADPH) (EC 1.8.1.2) was purified to homogeneity from cysJ266, a mutant strain lacking sulfite reductase flavoprotein. The siroheme- and Fe4S4-containing enzyme was isolated as a monomeric 63-kDa polypeptide and consisted of a mixture of unligated enzyme and a complex with sulfite. Following reduction with 5'-deazaflavin-EDTA and reoxidation, the complex was converted to the uncomplexed, high spin ferri-siroheme state seen previously with Escherichia coli sulfite reductase hemoprotein preparations. The S. typhimurium hemoprotein exhibited catalytic and physical properties identical to the hemoprotein prepared by urea dissociation of E. coli sulfite reductase holoenzyme and was fully competent in reconstituting NADPH-sulfite reductase activity when combined with excess purified sulfite reductase flavoprotein. The DNA sequences of cysI and cysH from S. typhimurium and E. coli B were determined and, together with previously reported data, confirmed the organization of this region as promoter-cysJ-cysI-cysH with all three genes oriented in the same direction from the promoter. Molecular weights deduced for the cysI-encoded sulfite reductase hemoprotein and for the cysH-encoded 3'-phosphoadenosine 5'-phosphosulfate sulfotransferase were approximately 64,000 and 28,000, respectively. Comparison of the deduced amino acid sequence of sulfite reductase hemoprotein with that of spinach nitrite reductase (Back, E., Burkhart, W., Moyer, M., Privalle, L., and Rothstein, S. (1988) Mol. Gen. Genet. 212, 20-26), which also contains siroheme and an Fe4S4 cluster, showed two groups of cysteine-containing sequences with the structures Cys-(X)3-Cys and Cys-(X)5-Cys, which are homologous in the two enzymes and are postulated to provide the ligands of the Fe4S4 cluster in both proteins. From these sequences and from crystallographic (McRee, D. E., Richardson, D. C., Richardson, J. S., and Siegel, L. M. (1986) J. Biol. Chem. 261, 10277-10281) and spectroscopic data in the literature, a model is proposed for the structure of the active center of these two enzymes.
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PMID:Characterization of the cysJIH regions of Salmonella typhimurium and Escherichia coli B. DNA sequences of cysI and cysH and a model for the siroheme-Fe4S4 active center of sulfite reductase hemoprotein based on amino acid homology with spinach nitrite reductase. 267 Sep 46

The localization of enzymes of assimilatory sulfate reduction was examined in roots of 5-d-old pea (Pisum sativum L.) seedlings. During an 8-h period, roots of intact plants incorporated more label from (35)SO 4 (2-) in the nutrient solution into the amino-acid and protein fractions than shoots. Excised roots and roots of intact plants assimilated comparable amounts of radioactivity from (35)SO 4 (2-) into the amino-acid and protein fractions during a 1-h period, demonstrating that roots of pea seedlings at this stage of development were not completely dependent on the shoots for reduced sulfur compounds. Indeed, these roots contained activities of ATP-sulfurylase (EC 2.7.7.4), adenosine 5'-phosphosulfate sulfotransferase, sulfite reductase (EC 1.8.7.1) and O-acetyl-L-serine sulfhydrylase (EC 4.2.99.8) at levels of 50, 30, 120 and 100%, respectively, of that in shoots. Most of the extractable activity of adenosine 5'-phosphosulfate sulfotransferase was detected in the first centimeter of the root tip. Using sucrose density gradients for organelle separation from this part of the root showed that almost 40% of the activity of ATP-sulfurylase, adenosine 5'-phosphosulfate sulfotransferase and sulfite reductase banded with the marker enzyme for proplastids, whereas only approximately 7% of O-acetyl-L-serine sulfhydrylase activity was detected in these fractions. Because their distributions on the gradients were very similar to that of nitrite reductase, a proplastid enzyme, it is concluded that ATP-sulfurylase, adenosine 5'-phosphosulfate sulfotransferase and sulfite reductase are also exclusively or almost exclusively localized in the proplastids of pea roots. O-Acetyl-L-serine sulfhydrylase is predominantly present in the cytoplasm.
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PMID:Localization of enzymes of assimilatory sulfate reduction in pea roots. 2420 22