Understanding Deuterium-labeling in Palmitic Acid Synthesis using Fatty Acid Synthase, NADPH and Malonyl-CoA Enzyme System.

You are investigating the incorporation of deuterium from [2-2H]acetyl-CoA (all hydrogen atoms replaced by deuterium) into palmitic acid with two different enzyme systems as described below. Predict which hydrogen atoms of palmitic acid will be deuterium-labeled in each system by clicking on each hydrogen that will be labeled. (Selected hydrogens will turn green. You can deselect by clicking a second time. Be careful to select only H atoms, and not bonds.) The enzyme system contains fatty acid synthase, NADPH, and unlabeled malonyl-CoA.

all of the H’s on the terminal CH3 are highlighted

As deuterium from [2-2H]acetyl-CoA is incorporated into palmitic acid with two different enzyme systems, we need to predict which hydrogen atoms of palmitic acid will be deuterium-labeled in each system.

In the given enzyme system containing fatty acid synthase, NADPH, and unlabeled malonyl-CoA, the labeled deuterium would be incorporated at the α-position (alpha-position) of the growing palmitic acid chain during each cycle of elongation in fatty acid synthesis.

Therefore, the following hydrogen atoms (H) in palmitic acid would be deuterium-labeled:

1. Hα of the first acetyl-CoA unit (the methyl group at the beginning of the chain)
2. Hα of the second acetyl-CoA unit (i.e., the next methyl group in the chain, after the first cycle of elongation)
3. Hα of the third acetyl-CoA unit (i.e., the third methyl group in the chain, after two cycles of elongation)
4. And so on, until Hα of the 16th acetyl-CoA unit

So, in this enzyme system, all the α-hydrogens (Hα) of palmitic acid would be deuterium-labeled.

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