Nudix (for nucleoside diphosphates linked to some moiety X) hydrolases act to hydrolyze ribonucleoside and deoxyribonucleoside triphosphates, nucleotide sugars, coenzymes, or dinucleoside polyphosphates. Arabidopsis (Arabidopsis thaliana) contains 27 genes encoding Nudix hydrolase homologues (AtNUDX1 to -27) with a predicted distribution in the cytosol, mitochondria, and chloroplasts. Previously, cytosolic Nudix hydrolases (AtNUDX1 to -11 and -25) were characterized. Here, we conducted a characterization of organelle-type AtNUDX proteins (AtNUDX12 to -24, -26, and -27). AtNUDX14 showed pyrophosphohydrolase activity toward both ADP-ribose and ADP-glucose, although its K m value was approximately 100-fold lower for ADP-ribose (13.0 6 0.7 mM) than for ADP-glucose (1,235 6 65 mM). AtNUDX15 hydrolyzed not only reduced coenzyme A (118.7 6 3.4 mM) but also a wide range of its derivatives. AtNUDX19 showed pyrophosphohydrolase activity toward both NADH (335.3 6 5.4 mM) and NADPH (36.9 6 3.5 mM). AtNUDX23 had flavin adenine dinucleotide pyrophosphohydrolase activity (9.1 6 0.9 mM). Both AtNUDX26 and AtNUDX27 hydrolyzed diadenosine polyphosphates (n = 4-5). A confocal microscopic analysis using a green fluorescent protein fusion protein showed that AtNUDX15 is distributed in mitochondria and AtNUDX14 -19, -23, -26, and -27 are distributed in chloroplasts. These AtNUDX mRNAs were detected ubiquitously in various Arabidopsis tissues. The T-DNA insertion mutants of AtNUDX13,, and -27 did not exhibit any phenotypical differences under normal growth conditions. These results suggest that Nudix hydrolases in Arabidopsis control a variety of metabolites and are pertinent to a wide range of physiological processes.

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Background: ClpC/Hsp93 is a chloroplast molecular chaperone whose function is essential for plant viability. Results: Chloroplast ClpC localized in both the stromal and envelope-membrane fractions associates with the Clp proteolytic core. Conclusion: ClpC functions primarily as the chaperone component of the chloroplast Clp protease. Significance: Learning how ClpC contributes to key functions of the Clp protease is crucial to understanding the importance of this essential enzyme for chloroplast biology.

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