Participation of Sulfhydryl Groups in Fatty Acid Synthesis by Chloroplast Preparations

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Abstract
Preparations of broken spinach chloroplasts incorporate acetate and malonate into long chain fatty acids. Avidin inhibits the incorporation of acetate but not of malonate. The ability to catalyze the incorporation of these precursors declines as the preparations age. This deterioration is associated with the soluble enzymes, rather than the fragments of the chloroplasts. The aging effect can be prevented to some extent by glutathione, which also alters the composition of the labeled fatty acids, favoring stearate and decreasing palmitate and oleate. Sulfhydryl reagents (p-chloromercuri-benzoate, Cd ions, arsenite) inhibit the incorporation of acetate and malonate into lipid. At higher concentrations the sulfhydryl reagents inhibit the incorporation into non-volatile water soluble compounds. The inhibition of p-chloromercuribenzoate and Cd ions can be reversed by reduced glutathione. The inhibition by arsenite is enhanced by the presence of 2,3-dimercaptopropanol.