Abstract
Enzymic activity of bee venom phospholipase A 2 has been studied at high temperatures using dispersed egg yolk and sonicated dipalmitoyl and dicaproyl lecithins as substrates. With egg yolk substrate the maximum activity was observed at 65°C and both dipalmitoyl and dicaproyl lecithins gave a maximum at 60°C. At 60°C the enzyme showed loss of activity in the presence of 0·7 M urea. The loss of activity at ca. 60°C could be due to the physical change in the nature of the substrates and/or due to the denaturation of enzyme at this temperature. Preincubation of enzyme at temperatures up to 90°C for 45 min gave the same temperature optimum of 65°C with egg yolk substrate which shows that the heat denaturation, if it occurs, is reversible. O.R.D. studies of pure bee venom phospholipase A 2 showed no change in optical rotation from 10 to 90°C. In spite of the constant optical rotatory dispersion of the protein up to 90°C, sudden loss of enzyme activity was noticed above 60°C with the lecithin substrates.
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