COALESCENCE AS A FACTOR IN SOLVENT STIMULATION OF PLASTID PHOSPHATIDASE C ACTIVITY

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Abstract
Solvents which stimulate plastid phosphatidase C activity (e.g., ethyl ether, propyl ketone, and ethyl butyrate) have been observed (microscopically) to produce coalescence of lecithin and chloroplast phases, while those which do not stimulate the reaction (e.g., chloroform and petroleum ether) do not produce coalescence. In the ethyl ether-stimulated reaction, all of the original enzymatic activity was associated with the coalesced material, and the lecithin apparently formed an ether-insoluble complex with the chloro-plasts; no enzymatic activity appeared in either the aqueous or ether phases. Ether extraction of chloroplasts alone did not liberate the enzyme from the plastids, and the presence of this stimulating solvent was still necessary for reaction with the substrate to occur. It is concluded that stimulating solvents achieve their effect primarily by causing substrate and plastid phases to coalesce and that the enzymatic reaction actually proceeds in the coalesced phase.