MTHFR, or Methylenetetrahydrofolate reductase, is an enzyme that plays a crucial role in the catalysis of the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate. This reaction is part of the folate metabolism pathway, which is essential for the body's ability to convert homocysteine into methionine. Methionine is a critical amino acid required for protein synthesis and various other cellular functions.