The NADH diphosphatase encoded by the Saccharomyces cerevisiae NYP1 nudix hydrolase gene is located in peroxisomes

The NPY1 nudix hydrolase gene of Saccharomyces cerevisiae has been cloned and shown to encode a diphosphatase (pyrophosphatase) with NADH as the preferred substrate, giving NMNH and AMP as products. NADPH diadenosine diphosphate, NAD(+), NADP(+), and ADP-ribose were also utilized efficiently. K-m values for NADH, NAD(+), and ADP-ribose were 0.17, 0.5, and 1.3 mM and k(cat) values 1.5, 0.6, and 0.6 s(-1), respectively. NPY1 has a potential C-terminal tripeptide PTSI peroxisomal targeting signal (SHL). By fusing NPY1 to the C-terminus of yeast-enhanced green fluorescent protein, the enzyme was found to be targeted to peroxisomes. Colocalization with peroxisomal thiolase was also shown by indirect immunofluorescence. Related sequences in other organisms also have potential PTSI signals, suggesting an important peroxisomal function for this protein. This function may be the regulation of nicotinamide coenzyme concentrations independently of those in other compartments or the elimination of oxidized nucleotide derivatives from the peroxisomal environment. (C) 2001 Academic Press.