NE is converted to EPI via PNMT, which is induced by cortisol.
I just tried to think of what's released by the Adrenal Medulla (Epinephrine). PNMT is the only choice that made sense.
The frustrating thing about this is that if you are familiar the biochem, you can get really stuck between D and E.
D would really be assocaited with SuccinylCoa Synthesis, as Methylmalonyl-Coa is the precurser to SuccinylCoa, which is an important gluconeogenic intermediary. Knowledge of biochem could make you think that the racemase is an important intermediary enzyme that is required for the MMA-mutase to even work (i.e. the product of PropionylCarboxylase is not the right chiral structure for it to work, hence the need for a racemase).
Ultimately, although the logic stands, I guess its better to go down the route of less logical leaps. It is better to know that hypoglycemia leads to neurogenic and neuroglycopenic Sx, the former being the autonomic response to increase glycemia. In that case, epi, which is an importnt hormone that metabolizes energy, is needed. PNMT generates Epi from NE.
submitted by โperidot(115)
In case anyone else was wondering about the other choices:
A: Acetyl-CoA carboxylase is the first committed step in fatty acid synthesis
B: Homocysteine methyltransferase turns homocysteine into methionine (we can deduce this from knowledge about homocystinuria)
C: Methionine adenosyltransferase makes SAM. SAM has two roles that we know of - one in turning methionine back into homocysteine, and one turning norepinephrine into epinephrine. This could make it a tempting choice but at the time I just saw the word 'methionine' and thought that couldn't have anything to do with cortisol/catecholamines.
D: LOL for methylmalonyl-CoA racemase, wiki says "It is routinely and incorrectly labeled as 'methylmalonyl-CoA racemase'. It is not a racemase because the CoA moiety has 5 other stereocenters." Good job NBME. Anyway, methylmalonyl-CoA epimerase is involved in the same catabolic pathway that we know of through propionic acidemia, so it's involved in breakdown of fatty acids and amino acids.