Purine biosynthesis and catabolism in soybean root nodules: Incorporation of 14C from 14CO 2 into xanthine

Abstract

Nodulated root systems of soybean plants were exposed to 14CO 2 in the presence and absence of allopurinol. After 5 h about one-fifth of the label in the perchloric acid-soluble fraction of the nodules was found to be in xanthine in the allopurinol-treated plants. Control plants contained much lower levels of xanthine, but with similar specific activity. Hypoxanthine was not detected in either control or allopurinol-treated plants, even though it would be expected to accumulate in the latter. Degradation of labeled xanthine from allopurinol-treated plants using xanthine oxidase and uricase resulted in the loss of most of the label. The preferential incorporation and accumulation of 14C from 14CO 2 into C 6 of xanthine in allopurinol-treated plants is consistent with the involvement of phosphoribosylaminoimidazole carboxylase in the de novo synthesis of purines. The accumulation of xanthine and absence of hypoxanthine in nodules of allopurinol-treated plants confirms earlier observations. In addition, the similar specific activities of 14C in xanthine in allopurinol-treated and control plants indicate that the xanthine which accumulates in allopurinol-treated plants is the product of de novo purine biosynthesis.