Greer W L, Pendyala L, Wellman A M
Can J Biochem. 1980 May;58(5):369-76. doi: 10.1139/o80-048.
Two aspects of guanosine metabolism in Neurospora have been investigated. (a) The inability of adenine mutants (blocked prior to IMP synthesis) to use guanosine as a nutritional supplement; and (b) the inhibitory effect of guanosine on the utilization of hypoxanthine as a purine source for growth by these mutants. Studies on the utilization of guanosine indicated that the proportion of adenine derived from guanosine may be limiting for the growth of adenine mutants. In wild type, adenine is produced through the biosynthetic pathway when grown in the presence of guanosine. The amount of adenine produced through the de novo biosynthesis in wild type increases with increasing concentrations of guanosine in the medium. However, the total purine synthesis does not increase. Guanosine inhibits the uptake of hypoxanthine severely. In addition, guanosine and its nucleotide derivatives also inhibit the hypoxanthine phosphoribosyltransferase activity, at the same time stimulating the adenine phosphoribosyltransferase activity. Guanosine's effects on the uptake of hypoxanthine and its conversion to the nucleotide form may be the reasons why guanosine inhibits the utilization of hypoxanthine but not adenine by these mutants.
人们已经对粗糙脉孢菌中鸟苷代谢的两个方面进行了研究。(a) 腺嘌呤突变体（在肌苷酸合成之前受阻）无法将鸟苷用作营养补充剂；以及 (b) 鸟苷对这些突变体利用次黄嘌呤作为嘌呤源进行生长的抑制作用。对鸟苷利用的研究表明，源自鸟苷的腺嘌呤比例可能限制了腺嘌呤突变体的生长。在野生型中，当在鸟苷存在的情况下生长时，腺嘌呤通过生物合成途径产生。野生型中通过从头生物合成产生的腺嘌呤量随着培养基中鸟苷浓度的增加而增加。然而，总嘌呤合成并未增加。鸟苷严重抑制次黄嘌呤的摄取。此外，鸟苷及其核苷酸衍生物还抑制次黄嘌呤磷酸核糖转移酶活性，同时刺激腺嘌呤磷酸核糖转移酶活性。鸟苷对次黄嘌呤摄取及其转化为核苷酸形式的影响可能是鸟苷抑制这些突变体利用次黄嘌呤而不抑制腺嘌呤的原因。
