Schork S M, Bee G, Thumm M, Wolf D H
Institut für Biochemie, Universität Stuttgart, Germany.
FEBS Lett. 1994 Aug 1;349(2):270-4. doi: 10.1016/0014-5793(94)00668-7.
Fructose-1,6-bisphosphatase, a key enzyme in gluconeogenesis, undergoes catabolite inactivation when glucose is added to gluconeogenetically active cells of the yeast Saccharomyces cerevisiae. Phosphorylation of the enzyme is followed by rapid degradation. To elucidate the cellular proteolytic system involved in catabolite-triggered degradation of fructose-1,6-bisphosphatase this event was followed in different protease-deficient yeast mutants. In a mutant defective in the proteolytic function of the vacuole the degradation rate of the enzyme is not diminished. In contrast mutants defective in the proteolytic activity of the proteasome exhibit a strongly reduced glucose-induced degradation of fructose-1,6-bisphosphatase as compared to their isogenic wild-type counterparts. Our studies suggest that catabolite inactivation of fructose-1,6-bisphosphatase occurs in the cytosol, the degradation event being mediated by the proteasome. An explanation is presented which tries to resolve the formerly conflicting results, which suggested glucose-triggered uptake of fructose-1,6-bisphosphatase into the vacuole followed by vacuolar proteolysis.
果糖-1,6-二磷酸酶是糖异生途径中的关键酶，当向产糖异生活性的酿酒酵母细胞中添加葡萄糖时，该酶会发生分解代谢失活。酶的磷酸化之后会迅速降解。为了阐明参与分解代谢触发的果糖-1,6-二磷酸酶降解的细胞蛋白水解系统，在不同的蛋白酶缺陷型酵母突变体中跟踪了这一事件。在液泡蛋白水解功能有缺陷的突变体中，该酶的降解速率并未降低。相比之下，与同基因野生型对应物相比，蛋白酶体蛋白水解活性有缺陷的突变体中，葡萄糖诱导的果糖-1,6-二磷酸酶降解显著降低。我们的研究表明，果糖-1,6-二磷酸酶的分解代谢失活发生在细胞质中，降解过程由蛋白酶体介导。本文提出了一种解释，试图解决以前相互矛盾的结果，这些结果表明葡萄糖触发果糖-1,6-二磷酸酶被液泡摄取，随后进行液泡蛋白水解。
