11.21 Vitamin B12 Functions

Vitamin B12 is a cofactor for 2 enzymes:

1. Methionine synthase

2. Methylmalonyl mutase

Methionine Synthase

Methionine synthase is an important enzyme in 1-carbon metabolism that uses methylcobalamin as its cofactor and converts homocysteine to methionine by adding a methyl group. Methionine then is converted to other compounds that serve as methyl donors, as shown below1.

Figure 11.211 One-carbon metabolism

These methyl donors can donate methyl groups for methylating DNA, an epigenetic modification1.

Methymalonyl mutase

This enzyme uses adenosylcobalamin as its cofactor, and is important in the breakdown of odd chain fatty acids (5 carbons etc.). As you know, odd chain fatty acids are less common than even chain fatty acids, but this enzyme is required to properly handle these less common fatty acids1.


In addition to its role as a cofactor for enzymes, vitamin B12 is also important for preventing degradation of the myelin sheath that surrounds neurons, as shown below.

Figure 11.212 Vitamin B12 is needed to maintain the myelin sheath that surrounds neurons2

The mechanism through which vitamin B12 prevents demyelination is not known3.

References & Links

1. Byrd-Bredbenner C, Moe G, Beshgetoor D, Berning J. (2009) Wardlaw’s perspectives in nutrition. New York, NY: McGraw-Hill.

2. https://en.wikipedia.org/wiki/Myelin#/media/File:Neuron_Hand-tuned.svg

3. http://lpi.oregonstate.edu/infocenter/vitamins/vitaminB12/