Microsomal preparation from an animal tissue catalyzes release of carbon monoxide from a fatty aldehyde to generate an alkane.
Alkanes are widely distributed in nature and impaired alkane synthesis was implicated in certain neurological disorders. However, the mechanism of synthesis of alkanes in animals is unknown. Our search to find a convenient animal tissue to study alkane biosynthesis resulted in the finding that the uropygial gland (a modified sebaceous gland) of the eared grebe (Podiceps nigricollis) produces large amounts of alkanes. These alkanes, which constitute 35-41% of the total lipid produced, are mainly C21, C23, C25, and C27 n-alkanes. Cell free homogenates of this tissue synthesized alkanes from both fatty acid and aldehyde in the absence of O2. Differential centrifugation of the homogenates indicated that this activity was located in the microsomal fraction. With isolated microsomes conversion of fatty acid to alkane required CoA, ATP, and NADH whereas conversion of an aldehyde to alkane did not require the addition of cofactors. That the final step in alkane synthesis is a decarbonylation was shown by the stoichiometric production of heptadecane and CO from octadecanal. CO was identified by adsorption to RhCl [(C6H6)3P]3 and oxidation of the trapped CO to CO2 by watergas shift reaction. The enzyme preparation also catalyzed incorporation of 14C from 14CO into octadecanal showing the reversible nature of the decarbonylase. This decarbonylase had a sharp pH optimum at 7.0, a Kapp of 180 microM and a V1/2 of 90 rho mol/min/mg protein for octadecanal. The enzyme was inhibited by the metal chelators EDTA, O-phenanthroline, and 8-hydroxyquinoline, but not by KCN. It was stimulated nearly 3-fold by 5 microM 2-mercaptoethanol and inhibited by the presence of O2. During the conversion of [1-3H]octadecanal to heptadecane, 3H was lost to water and 3H from 3H2O was incorporated into the alkane generated from unlabeled octadecanal. The mechanism of the decarbonylation and the nature of the enzyme remain to be elucidated.
Cheesbrough
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TM
Ohio State Biotechnology Center, Ohio State University, Columbus 43210.
Kolattukudy
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PE
D000447:Aldehydes / Q000378:metabolism*; D000473:Alkanes / Q000378:metabolism*; D000818:Animals; D001717:Birds; D002248:Carbon Monoxide / Q000378:metabolism*; D005122:Exudates and Transudates / Q000032:analysis; D005227:Fatty Acids / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008861:Microsomes / Q000378:metabolism*; D012016:Reference Values; D012627:Sebaceous Glands / Q000378:metabolism* / Q000648:ultrastructure
D000447:Aldehydes; D000473:Alkanes; D005227:Fatty Acids; C001634:fatty aldehyde; D002248:Carbon Monoxide