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KMID : 1059520100540020208
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Journal of the Korean Chemical Society
2010 Volume.54 No. 2 p.208 ~ p.214
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Effect of Alcohols Toward the Transphosphatidylation Activity in Phospholipase D Catalyzed Reaction
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Koh Eun-Hie
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Abstract
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In the presence of alcohol, phospholipase D (PLD) is known to perform transphosphatidylation activity, during which the overall reaction rate of PLD increased. To elucidate the reaction mechanism of transphosphatidylation further, we investigated rate constants of transphosphatidylation reaction of the purified α-type PLD from cabbage in the presence of various alcohols. The second-oder rate constants of PLD transphosphatidylation showed a large increase with the primary alcohols examined as expected. In the case of butanol we observed the second-oder rate constant of 33.33 ± 1.33 M-1sec-1. This second-order rate constant of transphosphatidylation was as 400 times greater as the second-order hydrolysis rate constant of 0.078 M-1sec-1 which was adjusted for the water concentration. A linear free energy relationship between the pKa of alcohol and transphosphatidylation rate gives a Brønsted slope of βnu = 0.12 ± 0.03. This small βnu value implicates that the transition state of break down of phosphatidyl-enzyme intermediate (E-P) is likely dissociative. Finally, a reaction mechanism of cabbage PLD is suggested on the basis of our results presented here and the histidine residue known to be located in the active site of cabbage PLD.
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KEYWORD
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Phospholipase D, Transphosphatidylation, Effect of alcohol, Brønsted β value
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