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【多选题】
How are purine and pyrimidine bases recycled by salvage pathways?A.
Free purine and pyrimidine bases are constantly released in cells during the metabolic degradation of nucleotides. Free purines are in large part salvaged and reused to make nucleotides, in a pathway much simpler than the de novo synthesis of purine nucleotides described earlier.
B.
One of the primary salvage pathways consists of a single reaction catalyzed by adenosine phosphoribosyltransferase, in which free adenine reacts with PRPP to yield the corresponding adenine nucleotide.
C.
Free guanine and hypoxanthine (the deamination product of adenine ) are salvaged in the same way by hypoxanthine-guanine phosphoribosyltransferase.
D.
A similar salvage pathway exists for pyrimidine bases in microorganisms, and possibly in mammals.
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