Inouye K, Kuzuya K, Tonomura B
Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Biochim Biophys Acta. 1998 Oct 14;1388(1):209-14. doi: 10.1016/s0167-4838(98)00189-7.
Thermolysin, a thermophilic metalloproteinase, is markedly activated in the presence of high concentrations (1-5 M) of neutral salts. The activity increases in an exponential fashion with increasing salt concentration, and is enhanced 13-15 times with 4 M NaCl at pH 7.0 and 25 degreesC (K. Inouye, Effects of salts on thermolysin: activation of hydrolysis and synthesis of N-carbobenzoxy-l-aspartyl-l-phenylalanine methyl ester, and a unique change in the absorption spectrum of thermolysin, J. Biochem. 112 (1992) 335-340). In this study, the effect of NaCl on the thermal stability of thermolysin has been examined at 60-85 degreesC. The activation energy, Ea, for the thermal inactivation is 15 kcal/mol at 0 M NaCl, and increases up to 30-33 kcal/mol by the addition of 0. 5-1.5 M NaCl. Further increase in [NaCl] decreases the Ea value, and at 4 M NaCl it is almost the same as that at 0 M NaCl. Thermolysin at 0.5-1.5 M NaCl is twice as heat-stable as in the absence of NaCl. The NaCl dependence of the stability is different from that of the activity, suggesting that the effects of NaCl on activity and stability are independent. Thermolysin has been demonstrated to be not only a thermophilic enzyme but also a highly halophilic one.
嗜热菌蛋白酶是一种嗜热金属蛋白酶，在高浓度（1 - 5 M）中性盐存在的情况下会被显著激活。其活性随盐浓度的增加呈指数方式上升，在pH 7.0和25℃条件下，4 M氯化钠可使其活性增强13 - 15倍（K. 井上，盐对嗜热菌蛋白酶的影响：N - 苄氧羰基 - L - 天冬氨酰 - L - 苯丙氨酸甲酯水解和合成的激活以及嗜热菌蛋白酶吸收光谱的独特变化，《生物化学杂志》112 (1992) 335 - 340）。在本研究中，已在60 - 85℃下考察了氯化钠对嗜热菌蛋白酶热稳定性的影响。在0 M氯化钠时，热失活的活化能Ea为15 kcal/mol，添加0.5 - 1.5 M氯化钠后，Ea值增加至30 - 33 kcal/mol。氯化钠浓度进一步增加会使Ea值降低，在4 M氯化钠时，Ea值与0 M氯化钠时几乎相同。0.5 - 1.5 M氯化钠存在下的嗜热菌蛋白酶的热稳定性是无氯化钠时的两倍。氯化钠对稳定性的影响与对活性的影响不同，这表明氯化钠对活性和稳定性的影响是相互独立的。嗜热菌蛋白酶已被证明不仅是一种嗜热酶，也是一种高度嗜盐酶。
