Maassen A
Institut für Biochemie, Bereich Medizin (Charité), Humboldt-Universität, Berlin, FRG.
Biomed Biochim Acta. 1991;50(2):213-7.
Two sequence-homologous alpha-amylases from B. amyloliquefaciens and B. licheniformis were studied with respect to their stability against heat denaturation and were compared with respect to common structure-stabilizing principles. The investigated alpha-amylases were isolated from culture broth of B. amyloliquefaciens and B. licheniformis. The molecular parameters (molecular weight and isoelectric point) are similar. The thermostability was determined by changes of the protein structure (changes of the fluorescence emission spectra). At pH 5.0 the thermostable alpha-amylase from B. licheniformis showed a rate of denaturation which was achieved by the thermolabile alpha-amylase from B. amyloliquefaciens at a temperature 15 degrees lower. The alpha-amylase from B. licheniformis exhibits a marked stability also at the alkaline pH-range in contrast to the alpha-amylase from B. amyloliquefaciens. From measurements in the presence of EDTA and Ca2+ follows that both enzymes are stabilized by binding of calcium ions. An analysis of preferred amino acid exchanges between the two sequence-homologous alpha-amylases showed correspondences and differences to the well-known diagram of ARGOS. Possibly an increased thermic stability can already be achieved by special amino acid exchanges without significant changes in the protein structure.
对来自解淀粉芽孢杆菌和地衣芽孢杆菌的两种序列同源的α-淀粉酶进行了热变性稳定性研究，并根据常见的结构稳定原理进行了比较。所研究的α-淀粉酶是从解淀粉芽孢杆菌和地衣芽孢杆菌的培养液中分离出来的。其分子参数（分子量和等电点）相似。通过蛋白质结构的变化（荧光发射光谱的变化）来测定热稳定性。在pH 5.0时，地衣芽孢杆菌的热稳定α-淀粉酶的变性速率是解淀粉芽孢杆菌的热不稳定α-淀粉酶在低15摄氏度的温度下所达到的变性速率。与解淀粉芽孢杆菌的α-淀粉酶相比，地衣芽孢杆菌的α-淀粉酶在碱性pH范围内也表现出显著的稳定性。从在EDTA和Ca2+存在下的测量结果可知，两种酶都通过钙离子的结合而得到稳定。对这两种序列同源的α-淀粉酶之间优选的氨基酸交换进行分析，结果显示与著名的ARGOS图存在对应和差异。可能通过特殊的氨基酸交换，在蛋白质结构没有显著变化的情况下，就能已经实现热稳定性的提高。
