Lipase activity in some Cucubitaceae species

Lipase activity was demonstrated in the endosperm of three varieties of both germinated and ungerminated seeds of Cucubitaceae: white melon (Cucumeropsis manii naud); yellow melon (Colocynthis vulgaris); pumpkin (Cucurbita moschata). Fractionation of homogenates by centrifugation yields that fat layer (lipid bodies), supernatant (water soluble fraction), and particulate fraction (pellets) with lipase located in all the fractions. The highest activity was determined in the lipid body fraction. However, a mixture of the lipid bodies and supernatant gave a much higher activity than the lipid body alone. Preparation of the supernatant at different pH's (4.0–9.0) and treating the supernatant with different concentrations of (NH4) 2SO4, further separated the lipid bodies with separation increasing as pH increases from 6.0 – 9.0. Separation of lipid bodies did not occur below pH 4 no enzyme activity was detected in the supernatant after precipitation with 90% (NH4) 2SO4. Lipase was tightly bound to the lipid body membranes as it resisted solubilisation by repeated washing with buffers and NaCl solutions. Ultrasonication of the lipid bodies and treatment with diethyl-ether extracted triacylglycerols from the lipid bodies with lipase activity being recovered in the membrane fractions. Bio-Research Vol. 3(1) 2005: 66-7