In hepatic fatty acid oxidation, the enzyme enoyl-CoA hydratase acts on trans-2-enoyl-CoA to produce a specific stereoisomer of 3-hydroxyacyl-CoA. Which stereoisomeric form is produced, and why is this specificity important?

• A D(-)-3-hydroxyacyl-CoA; this isomer is directly oxidized by 3-hydroxyacyl-CoA dehydrogenase
• B D(-)-3-hydroxyacyl-CoA; this isomer must first be epimerized before further oxidation
• C L(+)-3-hydroxyacyl-CoA; this isomer is converted to ketone bodies directly
• D L(+)-3-hydroxyacyl-CoA; this isomer is directly oxidized by 3-hydroxyacyl-CoA dehydrogenase ✓

Explanation

Enoyl-CoA hydratase stereospecifically produces L(+)-3-hydroxyacyl-CoA (also written as S-3-hydroxyacyl-CoA) from trans-2-enoyl-CoA. This L-stereoisomer is the specific substrate for the next enzyme in beta-oxidation, L-3-hydroxyacyl-CoA dehydrogenase (also called HAD), which oxidizes it to 3-ketoacyl-CoA using NAD+. Stereospecificity ensures metabolic fidelity and efficiency in the mitochondrial beta-oxidation spiral.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

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