149 ENZYMES OF PURINE NUCLEOTIDE METABOLISM IN MATURE RAT BRAlN NEURONS IN CULTURE

Abstract

Several enzymes of purine nucleotide metabolism were assayed in mature (10-14 days old) rat brain neurons in culture: No activity could be detected for xanthine oxidase and uricase. The cultures exhibited de novo nucleotide synthesis. The results indicate that purine nucleotides can be synthesized in the mature rat brain cultured cells by de novo and by salvage from hypoxanthine, adenine and adenosine. From the Vmax values of the enzymes and from the known Km values, it appears that the degradation of adenine nucleotides through deamination to IMP has a slightly better capacity than that through dephosphorylation to adenosine and that the capacity for adenosine salvage is better than that for its deamination. The absence of xanthine oxidase activity is in favor of hypoxanthine salvage to IMP, but the presence of guanase competes with the salvage of guanine.