Ma H, Bloom L M, Walsh C T, Botstein D
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
Mol Cell Biol. 1989 Dec;9(12):5643-9. doi: 10.1128/mcb.9.12.5643-5649.1989.
Saccharomyces cerevisiae mutants containing different point mutations in the HXK2 gene were used to study the relationship between phosphorylation by hexokinase II and glucose repression in yeast cells. Mutants showing different levels of hexokinase activity were examined for the degree of glucose repression as indicated by the levels of invertase activity. The levels of hexokinase activity and invertase activity showed a strong inverse correlation, with a few exceptions attributable to very unstable hexokinase II proteins. The in vivo hexokinase II activity was determined by measuring growth rates, using fructose as a carbon source. This in vivo hexokinase II activity was similarly inversely correlated with invertase activity. Several hxk2 alleles were transferred to multicopy plasmids to study the effects of increasing the amounts of mutant proteins. The cells that contained the multicopy plasmids exhibited less invertase and more hexokinase activity, further strengthening the correlation. These results strongly support the hypothesis that the phosphorylation activity of hexokinase II is correlated with glucose repression.
含有HXK2基因不同点突变的酿酒酵母突变体被用于研究己糖激酶II的磷酸化作用与酵母细胞中葡萄糖阻遏之间的关系。检测了显示不同己糖激酶活性水平的突变体的葡萄糖阻遏程度，以转化酶活性水平作为指标。己糖激酶活性水平和转化酶活性水平呈现出很强的负相关，有少数例外情况可归因于极不稳定的己糖激酶II蛋白。通过以果糖作为碳源测量生长速率来测定体内己糖激酶II的活性。这种体内己糖激酶II活性同样与转化酶活性呈负相关。将几个hxk2等位基因转移到多拷贝质粒中，以研究增加突变蛋白量的影响。含有多拷贝质粒的细胞表现出较低的转化酶活性和较高的己糖激酶活性，进一步加强了这种相关性。这些结果有力地支持了己糖激酶II的磷酸化活性与葡萄糖阻遏相关的假说。
