11.0 Introduction

Three B vitamins are involved in what is known as 1-carbon metabolism. This is the movement of a 1-carbon unit, usually a methyl group (CH₃) from one compound to another. It is similar to the movement of the amino group that occurs in transamination. As shown in the figure below, folate, vitamin B₁₂, and vitamin B₆ are the B vitamins involved in 1-carbon metabolism.

Figure 11.1 1-carbon metabolism depiction. 5-methyl tetrahydrofolate (THF) donates a methyl group to cobalamin forming methylcobalamin. Methylcobalamin donates a methyl group to homocysteine, forming methionine (amino acid). Alternatively, vitamin B₆ can be utilized to convert homocysteine into cysteine.

Vitamin B₆ has been covered already in the previous chapter, so this chapter is going to focus on folate and vitamin B₁₂. We will examine this figure in pieces, so that hopefully by the time this chapter is completed, you will understand the role of all these vitamins in 1-carbon metabolism.