DISTRIBUTION OF ENZYMES CLEAVING PYRIDINE NUCLEOTIDES IN ANIMAL TISSUES

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Abstract
The distribution of diphos-phopyridine nucleotide (DPN) and DPNH pyrophosphatases and DPNase in centrifugally prepared fractions of organs of several species of animals is reported. A DPNH pyrophosphatase found in the soluble fraction of pigeon and of rabbit liver did not split DPN but accounted for over 50% of the DPNH pyrophosphatase activity of the whole homogenates. All organs tested, including pigeon liver and rabbit liver, contained a microsomal pyrophosphatase that attacked both DPNH and DPN, but split DPNH faster than DPN. DPN pyrophosphatase and DPNase activity were generally concentrated in the microsomal fraction of liver, of kidney, and of brain. Considerable difference was found with respect to pH on the activity of DPNase from organs of different animals. Inhibition of mitochondrial and microsomal DPNH oxidation by nicotinamide was noted. The significance of some of the distribution patterns is discussed.