A lipase from photosynthetic cyanobacterium Spirulina platensis (Arthrospira) was purified by sequential operation of ammonium sulphate precipitation, dialysis, DEAE-Sepharose anion exchange chromatography, and Sepharose-6B gel filtration chromatography for the first time. This purification procedure resulted in 375-fold purification of lipase with 29.35% final yield. The purified lipase showed a prominent single band on SDS-PAGE. It is a monomeric protein of 45 kDa molecular weight and its isoelectric point is 5.9. The purified lipase exhibited maximal hydrolytic activity at a temperature of 45 degrees C and pH of 6.5. The values of K-m and V-max calculated from the Lineweaver-Burk plot using p-nitrophenyl palmitate (p-NPP) as hydrolysis substrate were 0.02 mM and 38.9 mu mol min(-1) mg(-1), respectively. The catalytic efficiency (k(cat)/K-m) of purified lipase was determined as 1.5 x 10(6) M-1 s(-1). The remaining activity of the lipase was about 95% of its original activity at 25 degrees C for 24 h of preincubation. However, the remaining activity was about 26% of the original activity at 45 degrees C for 24 h. The purified lipase appears to be unique since it cleaved triolein at only 3-position releasing 1,2-diolein. Lipase activity was stimulated by Ca2+, Mg2+, Zn2+, Triton X-100 and SDS, and inhibited by Li-+,Li- Fe2+, Mn2+, EDTA and PMSF. (C) 2009 Elsevier B.V. All rights reserved.