Volatile hydrocarbons from photosynthetic membranes containing different fatty acids.

A cell-free plant system was developed generating short-chain volatile hydrocarbons as markers of light-induced copper-mediated peroxidation of fatty acids present either as endogenous constituents of photosynthetic membranes or added exogenously. Different polyunsaturated fatty acids are present in the blue green algaeAnacystis nidulans, Anabaena variabilis andSpirulina platensis. The first species has no polyunsaturated acids. Thylakoids isolated from these algae produce different short-chain volatile hydrocarbons. The location of the double bond of dienoic or higher polyunsaturated fatty acids most distant from the carboxyl group determines the chain length of hydrocarbons evolved. Their number of C-atoms is the same as found beyond this double bond of the fatty-acid molecule (ω-1). This pattern of volatile hydrocarbons produced is in contrast to thermolytic cleavage. Malondialdehyde is formed only when at least 3 double bonds are present in the fatty acid. Peroxidation of endogenous thylakoidal and added fatty acids is completed within 24 hr; a maximum of 1% of the carbon skeleton can be recovered as volatile hydrocarbons.