Preiss-Handler pathway

NAPRT activity was originally described in the context of the mammalian Preiss—Handler pathway. The respective gene (j>ncB) encoding an approximately 45-kDa protein was cloned and sequenced from E. coli and... 

Deamidation of Nicotinic Add. Enzymes from microorganisms (185-188), insects (189), and birds have been found to deamidate nicotinamide to nicotinic acid (190). Recently, Sundaram et al. (191) have shown that a strain of Leuconostoc mesenteroides which will grow on nicotinic acid but not on nicotinamide, does not possess the deamidase and will not convert the pyridine amide to DPN. On the other hand, Saccharomyces cerevisiae will grow on both pyridine compounds, and the yeast contains the deamidase. These observations suggest that the route of synthesis of DPN from nicotinamide may involve the Preiss-Handler pathway, and that deamidation of nicotinamide occurs during the synthesis, which is also indicated by studies in the intact mouse (see Section III, A). 

A considerable advance in elaborating the pathway of pyridine coenzyme synthesis resulted from the contributions of Preiss and Handler (118, 1B6-1B8). Before discussing the experiments of these investigators, it may be of value to review some of the earlier work on the metabolism of nicotinic acid and nicotinamide in erythrocytes. It has been known for some time that nicotinic acid taken orally results in a significant increase in the pyridine nucleotide content of human red blood cells (1B9, ISO). When equal concentrations of nicotinamide were given under identical conditions, there was no effect on the erythrocyte DPN level. Isolated erythrocytes have also been found to show a rise in DPN when incubated with nicotinic acid and not with nicotinamide. However, incubation with nicotinamide leads to a marked accumulation of nicotinamide mononucleotide (ISl). In this connection, it is of importance to point out that the level of the DPN pyrophosphorylase is extremely low in the red blood cell (ISB). 

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