Question

One-carbon transfers. Which derivative of folate is a reactant in the conversion of (a) glycine into serine? (b) homocysteine into methionine?

Short answer

(a) 5,10-methylene-tetrahydrofolate, (b) 5-methyl-tetrahydrofolate.

Step-by-step solution

Understand Folate's Role

Folate derivatives participate in one-carbon transfer reactions, which are crucial in various biosynthetic pathways. These reactions involve the transfer of one-carbon units by tetrahydrofolate (THF), each being a specific form of THF carrying a different one-carbon unit.

Identify Derivative for Glycine to Serine

For glycine to serine conversion, folate involved needs to carry a hydroxymethyl group to donate. This is achieved by 5,10-methylene-tetrahydrofolate which transfers a methylene group to glycine, forming serine.

Identify Derivative for Homocysteine to Methionine

In the conversion of homocysteine into methionine, a methyl group needs to be transferred. This involves 5-methyl-tetrahydrofolate, which donates a methyl group converting homocysteine into methionine.

Key concepts

Folate Derivatives

Folate derivatives play a fundamental role in biochemical one-carbon transfer reactions. These derivatives are essentially various forms of folate, a type of B vitamin, converted into active forms that participate in different chemical transformations.
Folates are crucial for the synthesis, repair, and methylation of DNA. They act as carriers of one-carbon units such as methyl, methylene, and formyl groups. Each derivative of folate is tailored for specific reactions, providing flexibility and specificity in the biological processes they partake in.

• 5,10-methylene-tetrahydrofolate: Involved in the transfer of methylene groups.
• 5-methyl-tetrahydrofolate: Specialized for transferring methyl groups.

Tetrahydrofolate (THF)

Tetrahydrofolate (THF) is the central molecule in folate metabolism and one-carbon transfer reactions. It is derived from folic acid and acts as a versatile carrier of carbon fragments. The versatility of THF lies in the ability to bind and transfer one-carbon units in different oxidation states, which are important in biosynthetic reactions.
THF can bind carbon units as:

• Formyl groups (CHO)
• Methylene groups (CH₂)
• Methyl groups (CH₃)

This adaptability makes THF a critical component in the synthesis of nucleotides and amino acids, ensuring the proper functioning of cells.

Glycine to Serine Conversion

The conversion of glycine to serine is a notable reaction that utilizes one of the folate derivatives. During this process, 5,10-methylene-tetrahydrofolate plays a pivotal role by donating a methylene group.
Here’s how the conversion occurs:

• 5,10-methylene-THF transfers its methylene group to glycine.
• The reaction facilitates the incorporation of the methylene group into glycine.
• This transformation results in the production of serine.

This conversion is essential in cellular metabolism, contributing to the biosynthesis of proteins and other important biomolecules.

Homocysteine to Methionine Conversion

Converting homocysteine to methionine involves the transfer of a methyl group, facilitated by 5-methyl-tetrahydrofolate. This process is vital to maintain levels of methionine, an essential amino acid critical for protein synthesis and methylation reactions.
During the conversion:

• 5-methyl-THF provides a methyl group to homocysteine.
• The enzyme methionine synthase aids in this transfer.
• Homocysteine accepts the methyl group, forming methionine.

This conversion is crucial in the regulation of homocysteine levels, which if elevated, may contribute to cardiovascular diseases.