Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.7.1.2 (nitrate reductase)
 3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The major proteinase in maize (Zea mays) roots behaves as a serine endopeptidase. A possible physiological role of this enzyme could be in the turnover of nitrate reductase (NR) and, as such, it could be of great importance in regulating the assimilation of nitrate. The objective of this research was to elucidate the specificity and uniqueness of maize root proteinase. When bovine serum albumin and an NR purified from Chlorella vulgaris were used as substrates, the maize root proteinase exhibited a preference for cleavages such that the amino acid on the amino side of the scissile bond was alanine. This information was established by microsequence analysis of the N termini of proteolytic fragments, and carboxypeptidase Y analysis of the C termini of proteolytic fragments of substrates hydrolyzed by the proteinase. Cleavage occurred at the sequence Ala/Ala-Ala-Ala-Pro-Glu in Chlorella NR, and at the sequence Ala-Asp-Glu-Ser-His-Ala-Gln in bovine serum albumin. When bovine serum albumin was the substrate, the maize root proteinase yielded a peptide map that is unique relative to those created with the other serine endopeptidases elastase, trypsin, or chymotrypsin. Based on our data, the maize root proteinase appears to cleave peptide bonds at the carboxy side of alanine. Because of its specificity, it should have useful applications in protein chemistry.
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PMID:Characterization of a maize root proteinase. 827 5

Assimilatory nitrate reductase has been purified with 55% recovery from a Neurospora crassa nmr-1 nit-6 mutant, using a modification of a published procedure. It possesses one heme per 240 000 g, and subunits of mol. wt. 68 000. Upon digestion with chymotrypsin, a heme-binding domain was isolated by gel filtration; its visible spectrum was highly similar to that of cytochrome b(5). On SDS gels, the fraction showed two heme-containing bands of 10 000 and 12 5000 daltons; their amino acid composition was not very different, suggesting that they originated from the same region of the polypeptide chain. After S-carboxymethylation, the mixture of bands was submitted to cyanogen bromide cleavage, and the fragments were separated by h.p.l.c. The two largest fragments yielded an identical sequence upon automated degradation. This sequence (39 residues with some gaps) could be easily aligned with that of cytochrome b(5) starting close to the N terminus. These results are discussed in terms of the possible quaternary structure of N. crassa nitrate reductase, whose heme-binding domain proves to be another member of the family of b(5)-like cytochromes.
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PMID:On the presence of a heme-binding domain homologous to cytochrome b(5) in Neurospora crassa assimilatory nitrate reductase. 1645 80