Biswas N, Ghosh A K
Applied Biochemistry Department, Indian Institute of Chemical Biology, Calcutta.
Biochim Biophys Acta. 1997 Jun 6;1335(3):273-82. doi: 10.1016/s0304-4165(96)00145-6.
Logarithmically growing cells of S. cerevisiae contained high neutral trehalase (NT) activity while stationary-phase cells had high acid trehalase (AT) activity. Change in activity profile of AT and NT were different during growth under different conditions, particularly during growth in acetate medium and up to 1 h of germination period, but that for AT and isoaspartyl methyltransferase (IMT) were found to be almost identical. Concomitant increase in NT activity as well as increase in cAMP level was noticed at the onset of spore germination. Increase in AT and IMT activities as well as decrease in S-adenosyl-L-methionine (AdoMet) level were noticed during stationary phase of growth. Acidic polyacrylamide gel electrophoresis and subsequent autoradiography revealed that substrate of IMT was a protein of molar mass around 82 kDa which could be an AT. Methylated AT was found to be more active while non-methylated AT was relatively less active in comparison to the untreated sample. Since AT existed as an equilibrium mixture of protomer and oligomer, it was suggested that IMT catalysed carboxyl methylation might have some contribution towards the regulation of AT activity.
对数生长期的酿酒酵母细胞含有高活性的中性海藻糖酶（NT），而稳定期细胞具有高活性的酸性海藻糖酶（AT）。在不同条件下生长期间，尤其是在乙酸盐培养基中生长以及萌发期长达1小时的过程中，AT和NT的活性谱变化不同，但发现AT和异天冬氨酰甲基转移酶（IMT）的活性谱几乎相同。在孢子萌发开始时，观察到NT活性以及cAMP水平同时增加。在生长稳定期，观察到AT和IMT活性增加以及S-腺苷-L-甲硫氨酸（AdoMet）水平降低。酸性聚丙烯酰胺凝胶电泳及随后的放射自显影显示，IMT的底物是一种摩尔质量约为82 kDa的蛋白质，可能是AT。与未处理样品相比，甲基化的AT活性更高，而非甲基化的AT活性相对较低。由于AT以单体和寡聚体的平衡混合物形式存在，因此有人认为IMT催化的羧基甲基化可能对AT活性的调节有一定作用。
