Walsh M C, Smits H P, Scholte M, Smits G, van Dam K
E.C. Slater Institute, University of Amsterdam, The Netherlands.
Folia Microbiol (Praha). 1994;39(6):557-9. doi: 10.1007/BF02814107.
In a multiple deletion mutant hxt1deltahxt2deltahxt3delta hxt4deltasnf3delta of Saccharomyces cerevisiae growing on a 2% glucose, high-affinity glucose-uptake (low Km) was exhibited throughout growth on glucose in contrast to the wild-type, which exhibited the usual low-affinity to high-affinity transition as the glucose in the medium was consumed. Elevated levels of invertase activity throughout growth on glucose, in this mutant as compared to the wild-type, indicate that glucose repression may be impaired. However, in a mutant containing only the HXT2 gene (hxt1deltahxt3deltahxt4deltasnf3delta), invertase levels were similar to those in the wild-type. It is likely, therefore, that some of these putative glucose transporters, such as HXT2, also have regulatory roles in cellular metabolism. In triple hexose-kinase mutants, rapid (200-ms) measurements of initial glucose-uptake revealed high-affinity glucose uptake (Km approx. 2 mmol/L) while measurements on the slower 5-s scale clearly demonstrate that uptake is not linear over this longer period. These results suggest that this high-affinity component does not require a functional hexose-kinase.
在以2%葡萄糖为生长培养基的酿酒酵母多缺失突变体hxt1Δhxt2Δhxt3Δhxt4Δsnf3Δ中，与野生型不同，在整个葡萄糖生长过程中均表现出高亲和力葡萄糖摄取（低Km值），野生型会随着培养基中葡萄糖的消耗呈现出通常的从低亲和力到高亲和力的转变。与野生型相比，该突变体在整个葡萄糖生长过程中蔗糖酶活性水平升高，这表明葡萄糖阻遏可能受到损害。然而，在仅含有HXT2基因的突变体（hxt1Δhxt3Δhxt4Δsnf3Δ）中，蔗糖酶水平与野生型相似。因此，很可能这些假定的葡萄糖转运蛋白中的一些，如HXT2，在细胞代谢中也具有调节作用。在三重己糖激酶突变体中，对初始葡萄糖摄取的快速（200毫秒）测量显示出高亲和力葡萄糖摄取（Km约为2 mmol/L），而在较慢的5秒尺度上的测量清楚地表明，在这个较长时间段内摄取不是线性的。这些结果表明，这种高亲和力成分不需要功能性己糖激酶。
