NMNAT (nicotinamide 5´-mononucleotide adenylyltransferase; EC 2.7.7.1) catalyses the transfer of the adenylyl group from ATP to NMN to form NAD. We have cloned a novel human NMNAT cDNA, designated hNMNAT-2, from human brain. The cDNA contains a 924 bp open reading frame that encodes a 307 amino acid peptide that was expressed as a histidine-patch-containing thioredoxin fusion protein. Expressed hNMNAT-2 shared only 35% amino acid sequence homology with the human NMNAT enzyme (hNMNAT-1), but possessed enzymic activity comparable with hNMNAT-1. Using human genomic databases, hNMNAT-2 was localized to chromosome 1q25 within a 171 kb gene, whereas hNMNAT-1 is on chromosome 1p32–35. Northern blot analysis revealed highly restricted expression of hNMNAT-2 to brain, heart and muscle tissues, which contrasts with the wide tissue expression of hNMNAT-1; different regions of the brain exhibited differential expression of hNMNAT-2. Substitution mutations of either of two invariant residues, His-24 or Trp-92, abolished enzyme activity. Anti-peptide antibody to a unique epitope within hNMNAT-2 was produced, and immunohistochemical analysis of sections of normal adult human pancreas revealed that hNMNAT-2 protein was markedly expressed in the islets of Langerhans. However, the pancreatic exocrine cells exhibited weak expression of hNMNAT-2 protein. Sections of pancreas from insulinoma patients showed strong expression of hNMNAT-2 protein in the insulin-producing tumour cells, whereas acinar cells exhibited relatively low expression of hNMNAT-2 protein. These data suggest that the unique tissue-expression patterns of hNMNAT-2 reflect distinct functions for the isoforms in the regulation of NAD metabolism.
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Research Article|
January 15 2004
Characterization of human brain nicotinamide 5′-mononucleotide adenylyltransferase-2 and expression in human pancreas
Joel A. YALOWITZ
;
Joel A. YALOWITZ
*
Department of Biochemistry and Molecular Biology, Richard L. Roudebush Veterans Affairs Medical Center – 151, 1481 West Tenth Street, Indianapolis, IN 46202, U.S.A.
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Suhong XIAO
;
Suhong XIAO
†
Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, U.S.A.
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Mangatt P. BIJU
;
Mangatt P. BIJU
†
Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, U.S.A.
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Aśok C. ANTONY
;
Aśok C. ANTONY
†
Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, U.S.A.‡
Medicine Service, Richard L. Roudebush Veterans Affairs Medical Center, Indianapolis, IN 46202, U.S.A.
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Oscar W. CUMMINGS
;
Oscar W. CUMMINGS
§
Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, U.S.A.
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Mark A. DEEG
;
Mark A. DEEG
†
Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, U.S.A.‡
Medicine Service, Richard L. Roudebush Veterans Affairs Medical Center, Indianapolis, IN 46202, U.S.A.
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Hiremagalur N. JAYARAM
Hiremagalur N. JAYARAM
1
*
Department of Biochemistry and Molecular Biology, Richard L. Roudebush Veterans Affairs Medical Center – 151, 1481 West Tenth Street, Indianapolis, IN 46202, U.S.A.‡
Medicine Service, Richard L. Roudebush Veterans Affairs Medical Center, Indianapolis, IN 46202, U.S.A.1
To whom correspondence should be addressed, at the Department of Biochemistry and Molecular Biology (e-mail hjayaram@iupui.edu).
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Biochem J (2004) 377 (2): 317-326.
Article history
Received:
April 04 2003
Revision Received:
September 17 2003
Accepted:
September 29 2003
Accepted Manuscript online:
September 29 2003
Citation
Joel A. YALOWITZ, Suhong XIAO, Mangatt P. BIJU, Aśok C. ANTONY, Oscar W. CUMMINGS, Mark A. DEEG, Hiremagalur N. JAYARAM; Characterization of human brain nicotinamide 5′-mononucleotide adenylyltransferase-2 and expression in human pancreas. Biochem J 15 January 2004; 377 (2): 317–326. doi: https://doi.org/10.1042/bj20030518
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