Pendyala L, Wellman A M
Can J Microbiol. 1977 Oct;23(10):1394-403. doi: 10.1139/m77-208.
Conidia of wild-type Neurospora crassa, preincubated for 3 1/2 h in growth medium, showed a typical triphasic pattern of adenine uptake. The three phases consisted of a quick initial uptake, followed by a plateau phase, and then by a resume lowered uptake. A study of the relative influx and efflux of [14C] adenine showed that the plateau phase in fact is a period of transmembrane movement of adenine and adenine metabolites. The efflux during the plateau phase essentially cancelled out all the influx during the same period. The uptake curve derived after taking into account the effluxed portion of radioactivity indicated that the second phase represents a period of lowered uptake activity. The beginning of the lowered uptake activity during the second phase is correlated with the presence of a high intracellular level of ATP derived from exogenous [14C]adenine. At the end of the secod phase, the intracellular level of ATP is much smaller and the rate of adenine uptake increases again. Analysis of the acid-soluble pool after feeding [14C]adenine indicated the presence of other 14C-nucleotides, but no detectable levels of bases and nucleosides were present. However, chromatographic analysis of the medium indicated that efflux results essentially in the accumulation of bases. The significance of this finding in relation to efflux is discussed.
野生型粗糙脉孢菌的分生孢子在生长培养基中预孵育3.5小时后，呈现出典型的腺嘌呤摄取三相模式。这三个阶段包括快速的初始摄取，随后是平稳期，然后是摄取速率恢复降低。对[14C]腺嘌呤的相对流入和流出的研究表明，平稳期实际上是腺嘌呤和腺嘌呤代谢物跨膜移动的时期。平稳期的流出基本上抵消了同一时期的所有流入。考虑到放射性流出部分后得出的摄取曲线表明，第二阶段代表摄取活性降低的时期。第二阶段摄取活性降低的开始与源自外源性[14C]腺嘌呤的高细胞内ATP水平的存在相关。在第二阶段结束时，细胞内ATP水平要小得多，腺嘌呤摄取速率再次增加。在加入[14C]腺嘌呤后对酸溶性库的分析表明存在其他14C-核苷酸，但未检测到碱基和核苷水平。然而，对培养基的色谱分析表明，流出基本上导致碱基的积累。讨论了这一发现与流出相关的意义。
