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79 DEGRADATION OF PURINE NUCLEOSIDES BY MITOCHONDRIAL ENZYMES OF BOVINE LIVER

In recent years, it has been shown that mitochondria actively metabolize purine nucleosides. It is documented that both deoxyguanosine and deoxyadenosine are phosphorylated by mitochondrial enzymes. In the case of deoxyguanosine, intact mitochondria form dGMP, dGDP and dGTP. Herein we report that mitochondria are also involved in the degradation both deoxyguanosine and deoxyadenosine. When intact or fractured mitochondria are treated with deoxyadenosine, there is an immediate loss of the deoxynucleoside and a corresponding formation of deoxyinosine. A partially purified preparation of the mitochondrial adenosine deaminase activity was able to deaminate both adenosine and deoxyadenosine and a Lineweaver-Burk plot showed that an apparent Km for adenosine was 10μ M. AMP and dAMP were not substrates. When deoxyguanosine was added to either intact or fractured mitochondria it was transformed to guanine in addition to the above mentioned nucleotides. A partially purified preparation of mitochondrial purine nucleoside phosphorylase was shown to be active using inosine ae substrate. An apparent Km of 6μ M was measured. These data indicate that mitochondria play a role in the catabolism of purine nucleosides and thus suggest new opportunities for the study of cellular nucleoside metabolism.