The final step in hydrocarbon biosynthesis involves loss of CO from a fatty aldehyde. This decarbonylation is catalyzed by microsomes from Botyrococcus braunu. Among the several detergents tested for solubiliing the decarbonylase, octyl fi-glucoside (0.1%) was found to be the most effective and released 65% ofthe enzyme activity in soluble form. FPLC ofthe solubilized enzyme preparation with Superose 6 followed by ion-exchange FPLC with Mono Q resulted in 200-fold increase in specific activity with 7% recovery. The purified enzyme released nearly 1 mol of CO for each mol of hydrocarbon.SDS/PAGE of the enzyme preparation showed two protein bands of equal intensity at 66 and 55 kDa. The absorption spectrum of the enzyme with bands at 410 un, 425 um, 580 mn, and 620 un suggests the presence of a porphyrin. Electron microprobe analysis revealed that the enzyme contained Co. Purification of the decarbonylase from B. braunii grown in "CoC12 showed that 57Co coeluted with the decarbonylase.These results suggest that the enzyme contains Co that might be part of a Co-porphyrin, although a corrin structure cannot be ruled out. Co-protoporphyrin IX itself caused decarbonylation ofoctadecanal at 60'C, whereas the metal ion or protoporphyrin alone, or several other metal porphyrins, did not cause decarbonylation. These results strongly suggest that biosynthesis of hydrocarbons is effected by a microsomal Co-porphyrincontaining enzyme that catalyzes decarbonylation of aldehydes and, thus, reveal a biological function for Co in plants.Aliphatic nonisoprenoid hydrocarbons are ubiquitous in living organisms in both the plant and animal kingdoms (1, 2). Widespread occurrence of hydrocarbons in animals, accumulation of hydrocarbons under pathological conditions (3,4), demonstrated biosynthesis of hydrocarbons in mammalian nerve tissue (2), and decreased hydrocarbon synthesis associated with neurological disorders (5, 6) suggest important biological functions for this class of simple compounds.On the basis of the results obtained with specifically labeled precursors in higher plant tissues, it was proposed that n-hydrocarbons are produced by elongation of a fatty acid followed by the loss of the carboxyl carbon (7-9). Subsequent studies with insects (10) and mammals (2) supported this mechanism for alkane biosynthesis. Microsomal preparations from plant and animal tissues that generate alkanes have been shown to catalyze elongation offatty acids (11,12). The nature of the reaction that results in the loss of the carboxyl carbon remained obscure as the chemical nature of the immediate precursors of hydrocarbon was unknown until recently. Aldehydes with one carbon more than the alkanes were found to accumulate when hydrocarbon synthesis was inhibited by thiol compounds such as dithioerythritol (DTE) (13). In cell-free preparations that generate hydrocarbons, the observation that an aldehyde with one carbon more than the hydrocarbon was formed suggests that the aldehyde might be the immediate precursor of hydrocarbons (14). Ho...