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¹ Department of Molecular Biology and Genetics, Faculty of Science, Dicle University, 21280 Diyarbakır, Turkey DOI : 10.38042/biotechstudies.953514 - In this study, the intracellular β-galactosidases of Bacillus subtilis 4NK and Bacillus paralicheniformis 5NK isolated from Bingöl Binkap hot spring was partially purified and characterized. As a result of purification, the yield of the enzyme for B. subtilis 4NK was 85.2% and the purification fold was 2.8. The yield for B. paralicheniformis 5NK was 76.8% and the purification fold was 2.0. The optimum temperature of the enzyme was determined as 45 ºC for B. subtilis 4NK and 55 ºC for B. paralicheniformis 5NK and the optimum pH was 6.0 for both. In addition, in the thermal stability experiments even at the end of 120 min both enzymes were stable at 50 ºC. It was determined that the partially purified enzyme activity increased in the presence of iodoacetamide and phenylmethylsulfonylfluoride for B. subtilis 4NK, dithiothreitol, N-ethylenemaleimide and phenylmethylsulfonylfluoride for B. paralicheniformis 5NK. The metals were found to activate the enzyme at low concentrations of Co²⁺, Cd²⁺ and Mn²⁺ for B. subtilis 4NK, Cu²⁺ and Cd²⁺ were found to inhibit the enzyme at high rates for B. paralicheniformis 5NK. Km and Vmax values for 4NK and 5NK, respectively; 23.80 mM, 1.978 μmol/min and 5.61 mM, 1.869 μmol/min. Keywords : Bacillus subtilis 4NK Bacillus paralicheniformis 5NK β-galactosidase characterisation