When Dealing with Stable Isotopes of Carbon and Sulfur, Enzymes

Question

When dealing with stable isotopes of carbon and sulfur, enzymes tend to favor
A) the lighter isotope.
B) the heavier isotope.
C) the isotopes in about equal proportions.
D) either the lighter or the heavier isotope, depending on environmental conditions.

Accepted Answer

Enzymes most often favor the lighter isotopes of carbon and sulfur because they are slightly easier to use in metabolic reactions. This is known as the kinetic isotope effect, and it occurs because lighter isotopes typically bond more easily with other atoms.