Ghosh M, Nanda G
Department of Microbiology, Bose Institute, Calcutta, India.
FEBS Lett. 1993 Sep 20;330(3):275-8. doi: 10.1016/0014-5793(93)80887-z.
Heating of Aspergillus beta-xylosidase at 85 degrees C +/- 1 degree C and pH 5.5-6.0 (optimum for activity), causes irreversible, covalent thermoinactivation of the enzyme, involving oxidation of the thiol groups that are required for catalysis. Exogenous addition of cysteine, DTT, GSH and mercaptoethanol stabilizes the enzyme by extending its half-life. A similar effect is also exhibited by bivalent cations like Mg2+, Mn2+, Co2+, Ca2+ and Zn2+ while, on the other hand Cu2+ accelerates thermoinactivation. Chemical modification of crude beta-xylosidase with cross-linking agents like glutaraldehyde or covalent immobilization to a nonspecific protein like gelatin and BSA also enhances enzyme thermostability. These results suggest that addition of thiols and bivalent metal ions to a crude beta-xylosidase preparation or immobilization/chemical modification enhances its thermal stability, thus preventing loss of catalytic activity at elevated temperatures.
在85摄氏度±1摄氏度、pH值为5.5 - 6.0（酶活性的最适条件）下加热黑曲霉β-木糖苷酶，会导致该酶发生不可逆的共价热失活，这涉及到催化所需的巯基的氧化。外源添加半胱氨酸、二硫苏糖醇、谷胱甘肽和巯基乙醇可通过延长其半衰期来稳定该酶。二价阳离子如Mg2+、Mn2+、Co2+、Ca2+和Zn2+也表现出类似的效果，而另一方面，Cu2+会加速热失活。用交联剂如戊二醛对粗β-木糖苷酶进行化学修饰，或将其共价固定到明胶和牛血清白蛋白等非特异性蛋白质上，也能提高酶的热稳定性。这些结果表明，向粗β-木糖苷酶制剂中添加巯基和二价金属离子，或进行固定化/化学修饰，可提高其热稳定性，从而防止在高温下催化活性的丧失。
