The pyridine nucleotide cycle. Studies in Escherichia coli and the human cell line D98/AH2.
Year: 1981
Type: article
Abstract: Different metabolic steps comprise the pyridine nucleotide cycles in Escherichia coli and in the human cell line HeLa D98/AH2. An analysis of the 32P-labeling patterns in vivo reveals that in E. coli, pyrophosphate bond cleavage of intracellular NAD predominates, while in the human cell line, cleavage of the nicotinamide ribose bond predominates. In E. coli, intracellular NAD is processed differently from extracellular NAD. Conversion of intracellular NAD to nicotinic acid mononucleotide (NaMN) can be demonstrated in intact cells. We have also assayed and purified an enzyme, NMN deamidase, which converts NMN to NaMN. These data suggest that in E. coli, the predominant intracellular pyridine nucleotide cycle operative under our experimental conditions is: NAD leads to NMN leads to NaMN leads to NaAD leads to NAD Thus, a metabolic event requiring pyrophosphate bond cleavage of NAD, such as DNA ligation, initiates most NAD turnover. In the human cell line, the data are consistent with the following NAD turnover cycle: (formula, see text) Whereas in E. coli, ADP-ribosylation does not make a quantitatively important contribution, we suggest that in HeLa cells, ADP-ribosylation events initiate NAD turnover.
Source: Journal of Biological Chemistry
Authors: D. Hillyard, M. Rechsteiner, P. Manlapaz-Ramos, J.S. Imperial, L.J. Cruz, B.M. Olivera
Institution: University of Utah
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: hybrid
Estimated APC paid: $3,430
OpenAlex ID: W1583913377