Dev I K, Harvey R J
J Biol Chem. 1984 Jul 10;259(13):8394-401.
Serine hydroxymethyltransferase was synthesized as a constant fraction of total protein of Escherichia coli over a wide range of specific growth rates. This was observed in all strains when grown in glucose-limited chemostat cultures; in thymine-requiring mutants during thymidine-limited growth; and in met A and met B auxotrophs, defective in homocysteine biosynthesis, during methionine-limited growth. This behavior has been referred to by others as "metabolic control." In addition, the synthesis of serine hydroxy-methyltransferase was subject to specific active control mechanisms, which responded to the needs of the cell for purine biosynthesis, methylation reactions, as well as to serine limitation. Under purine limitation, the rate of enzyme synthesis increased with decreasing growth rate, that is with increasing purine limitation. During methionine-limited growth of met E and met F auxotrophs (mutants unable to methylate homocysteine) the rate of enzyme synthesis increased with a decrease in specific growth rate from 0.65 to 0.30 h-1 but declined with further decrease in growth rate. Under serine limitation the rate of enzyme synthesis remained proportional to the growth rate, but at a rate twice that observed in unrestricted or glucose-limited growth. When purines were added to unrestricted or glucose-limited cultures, the rate of enzyme synthesis decreased by 40%, but remained proportional to growth rate. Addition of methionine or serine alone had no effect.
在广泛的特定生长速率范围内，丝氨酸羟甲基转移酶的合成量占大肠杆菌总蛋白的比例恒定。在葡萄糖限制的恒化器培养中生长的所有菌株中都观察到了这一点；在胸腺嘧啶限制生长期间的胸腺嘧啶需求突变体中；以及在蛋氨酸限制生长期间，同型半胱氨酸生物合成有缺陷的met A和met B营养缺陷型中。其他人将这种行为称为“代谢控制”。此外，丝氨酸羟甲基转移酶的合成受到特定的活性控制机制的影响，这些机制对细胞嘌呤生物合成、甲基化反应以及丝氨酸限制的需求做出反应。在嘌呤限制下，酶合成速率随着生长速率的降低而增加，即随着嘌呤限制的增加而增加。在met E和met F营养缺陷型（无法将同型半胱氨酸甲基化的突变体）的蛋氨酸限制生长期间，酶合成速率随着比生长速率从0.65 h-1降至0.30 h-1而增加，但随着生长速率的进一步降低而下降。在丝氨酸限制下，酶合成速率与生长速率保持正比，但速率是在无限制或葡萄糖限制生长中观察到的两倍。当向无限制或葡萄糖限制的培养物中添加嘌呤时，酶合成速率降低了40%，但仍与生长速率成正比。单独添加蛋氨酸或丝氨酸没有影响。
