- A synthesis of a homologous series of highly radioactive photoreactive fatty acids has been developed. Oxidative cleavage of the cis double bonds of unsaturated fatty acids by NaIO4/OsO4 produced the omega-oxo fatty acids; subsequent reduction by [3H]NaBH4 afforded a series of highly radioactive [omega-3H]hydroxy fatty acids to which a variety of photoreactive probes can be readily attached. In this study, the m-diazirinophenoxy group was coupled to the omega-hydroxy groups of the fatty acids, yielding the omega-(m-diazirinophenoxy) derivatives of nonanoic, undecanoic, tridecanoic, and pentadecanoic acid. These photoreactive derivatives were incorporated by L-cells into their major phospholipids; in addition, a number of proteins were shown to be acylated by these fatty acids. The photoreactive group was shown to remain intact as indicated by the cross-linking of the resulting photoreactive phospholipids to other phospholipids as well as to a number of L-cell proteins upon photolysis. This procedure thus identifies integral membrane proteins and directly produces photoaffinity derivatives of those proteins normally acylated by fatty acids.