Aug 25, 1976

Mechanism of rat liver microsomal stearyl-CoA desaturase. Studies of the substrate specificity, enzyme-substrate interactions, and the function of lipid

The Journal of Biological Chemistry
H G EnochP Strittmatter

Abstract

The three purified proteins which are required for microsomal stearyl-CoA desaturation, NADH-cytochrome b5 reductase, cytochrome b5, and desaturase, have been combined with egg lecithin or dimyristyl lecithin vesicles to reconstruct a functional electron transport system capable of utilizing NADH and O2 in the desaturation of stearyl-CoA. Such preparations appear to consist of phospholipid vesicles which contain the three proteins bound to the outer surface of the vesicles. Acyl-CoA derivatives containing 12 to 19 carbon fatty acyl chains are required for desaturase activity while derivatives containing 9 to 20 carbons are capable of binding to the enzyme. Shorter chain acyl-CoA derivatives, free CoA, and free fatty acids do not appear to bind to the enzyme. Inhibition and analog studies suggest that the methylene chain of stearyl-CoA assumes an eclipsed ("gauche") conformation at carbon atoms 9,10 in the enzyme-substrate complex. Furthermore, isotope rate effects obtained with deuterated stearyl-CoA derivatives indicate that hydrogen removal is the rate-limiting step of desaturation. Stearyl-CoA binds to pure liposomes and desaturase-containing liposomes, and it is this form of stearyl-CoA which appears to be the substrate for...Continue Reading

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Mentioned in this Paper

Acyl CoA Desaturases
Structure-Activity Relationship
Cytochrome Reductases
Microsomes, Liver
Phosphatidylcholines
Cytochromes
Electron Microscopy
Niosomes
Stearoyl-CoA Desaturase
Deuterons

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