been reported (Izumi et al., 1990;

been reported (Izumi et al., 1990; Janssen et al., 1994; Gao and Breuil, 1995; Kim et al.,
1998; Lee et al., 1999). An extracellular Bacillus lipase isolated by Sidhu et al. (1998a,b) had an activity optimum at 50
C. The enzyme had a half-life of 15 min at 75
C and it was stable to various oxidizing, reducing, and chelating agents. The enzyme was stable in the presence of surfactants and in organic solvents (Sidhu et al., 1998a,b). The crude lipase had an activity of 8.2 U/mL at 50
C and pH 8.0. The activity was further enhanced by the presence of Ca2+ (Sidhu et al., 1998a,b). Thermal stability of porcine pancreatic lipase has been discussed by Kiran et al. (2001b). Thermal stability of a lipase is obviously related with its structure (Zhu et al., 2001). Thermostability is influenced by environmental factors such as pH and the presence of metal ions. At least in some cases, thermal denaturation appears to occur through intermediate states of unfolding of the polypeptide (Zhu et al., 2001). Mutations in the ‘lid’ region of the enzyme can significantly affect heat stability (Zhu et al., 2001). Attempts are being made to proteinengineer lipases for improved thermal stability. Compared to the native enzyme, thermal and operational stability of many lipases can be significantly enhanced by immobilization (Xu et al., 1995; Reetz et al., 1996; Arroyo et al., 1999; Hiol et al., 2000). C. antarctica lipase B could be thermally stabilized by immobilization (Arroyo et al., 1999). The native enzyme and the covalently immobilized preparation appeared to follow different modes of thermal deactivation (Arroyo et al., 1999).
6.1. Effect of metal ions and chelating agents on lipase activity
Chartrain et al. (1993) observed that an extracellular lipase of P. aeruginosa MB5001 was
strongly inhibited by 1 mM ZnSO (94% inhibition) but was stimulated by adding 10 mM CaCl
2 4 (1.24-fold stimulation) and 200 mM taurocholic acid (1.6-fold stimulation). Mase et al.
(1995) studied the effect of metal ions (1 mM concentration) on a purified lipase of Pe. roqueforti IAM7268. The lipase activity was not affected by Ca Na+ ,K+ ,Cu2+ ,Na 2+ , EDTA, p-chloro mercuribenzoic acid, and iodoacetate (Mase et al., 1995). In contrast, the enzyme was inhibited by Ag+ ,Fe2+ ,Hg 2+ , and isopropyl fluorophosphate. In another similar study with metal ions (1 mM) and chelating agents, P. pseudoalcaligenes F-111 lipase activity was 60% inhibited by Fe 3+ but not by Ca 2+ ,Hg+ ,Mg 2+ , Cu2+ ,Mg2+2+,Co2+ ,Cd ,and Pb2+ (Lin et al., 1996). Metal chelators (EDTA, o-phenanthrolin) did not significantly affect the alkaline lipase activity (Lin et al., 1996). Sharon et al. (1998) reported a lipase of P. aeruginosa KKA-5 that retained its activity in presence of Ca2+ and Mg 2+ but was slightly inhibited by Mn2+ ,Cd 2+ , and Ba 2+ ,Zn , and Cu . Salts of heavy metals (Fe 2+ ,Zn 2+ ,Hg2+ ,Fe3+ ) strongly inhibited the lipase, suggesting that they were able to alter the enzyme conformation (Sharon et al., 1998). The effect of various metal ions on S. epidermidis lipase activity was reported by Simons et al. (1998). The enzyme needed calcium as a cofactor for catalytic activity (Simons et al., 1998). Biochemical characterization showed that this lipase was closely related to the lipase of
S. aurelis NCTC 8530. Both the enzymes had a pH optimum of around 6.0 and were quite
stable at low pH. Hiol et al. (2000) studied the effect of various compounds and enzyme 2+ 2+
,Mn ,Mn 2+ 2+ 2+
,