Hydroxy-butyryl-ACP

One of the steps in fatty-acid biosynthesis is the dehydration of (i )-3-hydroxy-butyryl ACP to give frans-crotonyl ACP. Does the reaction remove the pro-JR or the pro-5 hydrogen from C2 ... 

STEP 7 Dehydration of /3-hydroxy-butyryl ACP yields crotonyl ACP. 

STEPS 6-8 OF FIGURE 23.6 REDUCTION AND DEHYDRATION The ketone carbonyl group in acetoacetyl ACP is next reduced to the alcohol j8-hydroxy-butyryl ACP by j8-keto thioester reductase and NADPH. R Stereochemistry results at the newly formed chirality center in the )8-hydroxy thioester product. (Note that the systematic name of a butyryl group is butanoyl.)... 

Malonyl-ACP, formed from acetyl-CoA (shuttled out of mitochondria) and C02, condenses with an acetyl bound to the Cys—SH to yield acetoacetyl-ACP, with release of C02. This is followed by reduction to the D-/3-hydroxy derivative, dehydration to the trans-A2-unsaturated acyl-ACP, and reduction to butyryl-ACP. NADPH is the electron donor... 

Reduction and dehydration. The ketone carbonyl group in acetoacetyl ACP is next reduced to an alcohol by NADPH (nicotinamide adenine dinucleotide phosphate), a reducing coenzyme closely related to NADH. Subsequent dehydration of the resulting /3-hydroxy thiol ester (E2 reaction) in step 7 yields crotonyl ACP, and the carbon-carbon double bond of crotonyl ACP is further reduced by NADPH in step 8 to yield butyryl ACP. 

---