Hutter B, Dick T
Institute of Molecular and Cell Biology, Singapore, Singapore.
FEMS Microbiol Lett. 1998 Oct 1;167(1):7-11. doi: 10.1111/j.1574-6968.1998.tb13200.x.
The aerobic fast-growing Mycobacterium smegmatis has, like its slow-growing pathogenic counterpart M. tuberculosis, the capability to adapt to anaerobiosis by shifting down to a drug resistant dormant state. Here, we report the identification of the first enzyme, L-alanine dehydrogenase, whose specific activity is increased during dormancy development in M. smegmatis. This mycobacterial enzyme activity was previously identified as the 40-kDa antigen in M. tuberculosis and shows a preference for the reductive amination of pyruvate to alanine at physiological pH. The determination of the temporal profile of alanine dehydrogenase activity during dormancy development showed that the activity stayed at a low baseline level during the initial aerobic exponential growth phase (0.7 mU mg-1 min-1). After termination of aerobic growth, alanine dehydrogenase activity increased rapidly 5-fold. As oxygen becomes more and more limiting, the enzyme activity declined until it reached a level about two-third that of the peak value. The strong induction immediately after deflection from aerobic growth suggests that alanine might be required for the adaptation from aerobic growth to anaerobic dormancy. As alanine synthesis is coupled to NADH oxidation, we propose that the induction of alanine dehydrogenase activity might also support the maintenance of the NAD pool when oxygen as a terminal electron acceptor becomes limiting.
需氧快速生长的耻垢分枝杆菌，与其生长缓慢的致病性对应物结核分枝杆菌一样，具有通过转变为耐药休眠状态来适应厌氧环境的能力。在此，我们报告了第一种酶——L-丙氨酸脱氢酶的鉴定，其比活性在耻垢分枝杆菌休眠形成过程中有所增加。这种分枝杆菌酶活性先前在结核分枝杆菌中被鉴定为40 kDa抗原，并且在生理pH值下显示出对丙酮酸还原胺化生成丙氨酸的偏好。对休眠形成过程中丙氨酸脱氢酶活性的时间分布测定表明，在最初的需氧指数生长期，该活性保持在较低的基线水平（0.7 mU mg-1 min-1）。需氧生长终止后，丙氨酸脱氢酶活性迅速增加5倍。随着氧气变得越来越有限，酶活性下降，直至达到约为峰值三分之二的水平。从需氧生长转变后立即出现的强烈诱导表明，丙氨酸可能是从需氧生长适应厌氧休眠所必需的。由于丙氨酸合成与NADH氧化相偶联，我们提出，当作为末端电子受体的氧气变得有限时，丙氨酸脱氢酶活性的诱导也可能有助于维持NAD库。
