EFFECT OF CALCIUM IONS TO THE ACTIVITY AND STABILITY OF EXTRACELLULAR LIPASE PRODUCED BY MODERATE HALOPHILIC BACTERIA Halomonas meridiana BK-AB4

Abstract

This study reported the isolation and biochemical studies of extracellular lipase produced by a moderate halophilic bacterium, Halomonas meridiana BK-AB4. The estimated molecular weight of the lipase BK-AB4 is about 50 kDa. The study of metal ions effect to the enzyme activity revealed the strong dependency towards the presence of Ca²⁺ ion. Further studies showed that the optimum pH of the enzyme was similar in the presence and the absence of Ca²⁺ ions. However, the presence of Ca²⁺ ions could improve the enzyme thermal stability as indicated by the shift of its optimum temperature from 45°C - 50°C. The addition of Ca²⁺ ions was also enhancing residual activity towards various inhibitors, such as SDS and PMSF up to 55% and 68%, respectively. Another interesting effect of the addition of Ca²⁺ ions were noted when various organic solvents were added to the enzyme solution in the ratio of 1:1. The activity of the enzyme increased up to 122% and 126% relative to the control when methanol and n-butanol were added, respectively. This study thus showed that the addition of Ca²⁺ ion not only improved the catalytic activity of lipase BK-AB4 but also made the enzyme more tolerable against various perturbations.