Answer to Question #5087 in Biochemistry for saif

Question

How
many
tritium
atoms
(3H)
are
incorporated
into
palmitate
when
fatty
acid
synthesis
is
carried
out
in
vitro
with
the
following
labeled
substrate?
Explain
your
answer

Answer 1

Palmitate = palmitic acid with deprotonated carboxylic group (ionized form). It contains 16 atoms of carbon. 14 of them are bounded with two atoms of hydrogen (CH2). Terminal carbon (ω1) is in the form of methyl group (CH3). The carbon of carboxylic group (C1) doesn’t linked with hydrogen in deprotonated form. So, the total amount of hydrogen atoms required for the synthesis of palmitate can be calculated by the formula:
So, the total number of hydrogen atoms in the palmitate is 31. If we use protonated form of palmitic acid (with hydrogen in carboxylic group), the number is 32. But it must be stressed, that all forms of hydrogen (for example, NADPH+H+, H2O) that are used in the enzymatic synthesis of palmitate also must contain 3H-isotope. If not, the total number of incorporated 3H will be significantly less.
Tritium is a “heavy” isotope of hydrogen. It has 2 neutrons in the nucleus, so the mass of tritium atom (3H) is 3 Da instead of 1 Da of 1H.
Answer: the total number of hydrogen atoms in the palmitate is 31. If we use protonated form of palmitic acid (with hydrogen in carboxylic group), the total number is 32.