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In order to explore a substrate specificity for cabbage phospholipase D, we examined the PLD reactivity toward the phosphatidylcholines with different chain length of acyl groups. The selected acyl chains were the saturated fatty acid of C8:0, C12:0, C16:0, and C20:0. The reactivity of these phospholipids were dependent largely on the ratio of PC : SDS. The PC : SDS ratio showing the optimal PLD activity were found to be 1:1.4, 1:2.2, 1:2.5, and 1:3.6 respectively as the increase of the acyl chain length. Likewise the optimum temperature for the maximal PLD activity were altered markedly to 25℃, 30℃, 35℃, 45℃ when the length of acyl chains increased. On the contrary the pH and concentration of Ca2+ necessary for the optimum PLD activity were not altered significantly. The kinetic parameter Vmax for short acyl chain substrate was greater than the values for the longer acyl chain, which indicates the fastest rate of hydrolysis. By the same token, the reactivity of longer chain substrate became slower for the hydrolysis activity.
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