Question

Consider a preparation that contains all the enzymes and cofactors necessary for the biosynthesis of palmitate from added acetyl-CoA and malonyl-CoA.

(a) If [2-14C-2-3H]acetyl-CoA (see the left figure above) and an excess of unlabeled malonyl-CoA are added as substrates, how many 3H atoms are incorporated into every molecule of palmitate, and what are their locations? How many 14C atoms are incorporated and what are their locations?

(b) If unlabeled acetyl-CoA and an excess of [1,3-14C-2-3H]malonyl-CoA (see the right figure above) are added as substrates, how many 3H atoms are incorporated into every molecule of palmitate, and what are their locations? How many 14C atoms are incorporated and what are their locations?

(c) Suppose that both of the labeled molecules above were added as substrates, how many 3H atoms are incorporated into every molecule of palmitate, and what are their locations? How many 14C atoms are incorporated and what are their locations?

Answer 1

Answer a)

When an unlabelled Malonyl- CoA is added to the 14C acetyl CoA, total of two 3H atoms are added with the release of CO2 and addition of H2O. The 3H atom is added to the α carbon atom of the structure. 2 14C carbon atom are added to the 1^st carbon atom of the 14C acetyl CoA.

Answer b)

When unlabelled Acetyle –CoA is added to [1,3-14C-2-3H]Malonyl CoA, Total of three 3H atoms are added at the last carbon atom of the structure. Total of 2 carbon atoms are added to 14C malonyl CoA at the 14^th carbon atom.

Answer c)

When both labelled molecules are added as the substrate. Then total of three 3H atoms and 3 14C atoms are added to the Palmitate. The carbon atom is added to the β carbon and hydrogen atom is added to the last carbon atom to form Palmitate.