@misc{oai:niigata-u.repo.nii.ac.jp:00005266,
 author = {Kaneko, Kentaro},
 month = {Mar},
 note = {A new enzyme family, nucleotide pyrophosphatase/phosphodiesterase (NPP), which exhibits hydrolytic activity toward pyrophosphate and phosphodiester bonds of numerous nucleotides and nucleotide sugars, has been identified recently in both mono- and di-cotyledonous plants. However, the physiological functions of NPPs are still poorly understood. In my thesis, I investigated the enzymatic properties and localizations of different rice NPP isozymes and the mechanisms involved in the transport of NPP glycoproteins from the ER-Golgi system to the plastid in rice cells. Identification of 6 different NPP encoding genes in rice genome cDNAs corresponding to 6 different NPP encoding genes (NPP1-6) were identified and isolated from rice shoot cDNA libraries. NPP genes were located on chromosomes 3 (NPP3), 8 (NPP1), 9 (NPP6) and 12 (NPP2, 4, 5) in rice. From comparison of the deduced amino acid sequences of proteins the degrees of identity between NPP1 and other NPPs ranged between 61.1 and 71.6%. Computer-assisted analyses using SignalP and PSORT algorithms revealed that all the deduced NPP amino acid sequences contained cleavable hydrophobic N-terminal extension that act as potential signal peptide to the ER and putative N-glycosylation sites. NPP amino acid sequences are highly similar to those of metallophosphatases from Lupinus luteus and purple acid phosphatases from Arabidopsis thaliana. The overall data thus indicate that NPPs belong to a large family of structurally related nucleotide hydrolases. Purification and characterization of NPP isozymes NPP1, 2, 3 and 6 were purified from transgenic rice calli overexpressed with each NPP isozyme by using acid precipitation, lectin chromatography, anion exchange chromatography and ultrafiltration. NPP1 and 6 were shown to preferably cleave the starch precursor molecule, ADP-glucose, on the other hand, NPP2 favorably hydrolyzed nucleoside diphosphates and adenosine 5'-phosphosulfate. In contrast, NPP3 was highly specific to bis(p-nitrophenyl)phosphate and exhibited no quantifiable hydrolyzing activity toward ADP-glucose. NPPs displayed broad optimal pH and relatively high optimal temperature for enzyme activities, and all these were glycoprotein bearing the N-linked carbohydrate chains. Subcellular localization of NPP isozymes To determine the subcellular localization of NPP1, 2, 3 and 6, we produced rice cells stably transformed with NPP1-GFP, NPP2-GFP, NPP3-GFP or NPP6-GFP and subjected them to confocal microscopy analyses. Fluorescence distribution patterns of NPP1-GFP, NPP2-GFP and NPP6-GFP largely matched to that of chloroplast autofluorescence, however, most of the NPP3-GFP was distributed in extra-chloroplastic compartments, probably in the endomembrane system of the cells. The subcellular localization of NPP2 and 6 were further characterized by using onion epidermal cells transiently expressing NPP-GFP., 新潟大学大学院自然科学研究科, 平成23年3月23日, 新大院博（農）甲第109号, 新大院博（農）甲第109号},
 title = {Studies on physiological function and intercellular-targeting mechanisms of rice nucleotide pyrophosphatase/phosphodiesterase},
 year = {2011}
}