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De Novo Purine Biosynthesis in Intact Cells of Cucurbita pepo1

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The capacity of intact cells of roots excised from summer squash plants (Cucurbita pepo L. cv Early Prolific Straightneck) to synthesize purine nucleotides de novo was investigated. Evidence that purine nucleotides are synthesized de novo included: (a) demonstration of the incorporation of [1-14C]glycine, [2-14C]glycine, NaH14CO3, and H14COONa into total adenine nucleotides; (b) observation that the addition of azaserine or aminopterin, known inhibitors of de novo purine synthesis in other organisms, blocked the incorporation of these precursors into adenine nucleotides; and (c) demonstration that the purine ring synthesized from these precursors was labeled in a manner consistent with the pathway for de novo purine biosynthesis found in microorganisms and animal tissues. Under optimal conditions, the activity of this pathway in roots excised from 2-day-old squash plants was 244 ± 13 nanomoles (mean ± standard error, n = 17) NaH14CO3 incorporated into ∑Ade (the sum of the adenine nucleotides, nucleoside and free base) per gram tissue during the 3-hour incubation period.

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