Question

You have discovered a new mutation in fatty acid synthase that completely inhibits fatty acid biosynthesis. Your biochemical experiments reveal that an intermediate containing an alpha-beta trans double bond remains bound to the mutated fatty acid synthase. A mutation in which subunit/domain of fatty acid synthase could explain this observation? a) β-hydroxyacyl-ACP dehydrase (DH) b) Enoyl-ACP reductase (ER) c) β-ketoacyl-ACP synthase (KS) d) Site 1 protease (S1P) e) Site 2 protease (S2P)

Answer 1

Pathway of the biosynthesis of fatty acids

The alpha beta trans double bond is found in Trans delta 2 enoyl ACP. It is also known as alpha beta enoyl ACP. It acts as substrate for reaction no.6. When enzyme of reaction no.6 Enoyl reductase is mutated, then alpha beta enoyl ACP will not be able to proceed further and hence remain as such. Therefore answer to the question is option b.

Option a:- beta hydroxyacyl dehydratase is enzyme found in reaction no.5. If it gets mutated the substrate Beta Hydroxyacyl ACP will remain as such.

Option c:- beta ketoacyl synthase that is enzyme of reaction no.3. Acetylmalonyl CoA will remain formed .

Option d:- Site 1 protease. It is functional mainly in sterols pathway. It cleaves endoplasmic reticulum loop of SREBP binding proteins transcription factors.

Option e:-Site 2 protease. It cleaves the membrane bound transcription factors.