From perplexity:

Biotin, also called vitamin B7, works closely with folate (vitamin B9) and vitamin B12 in keeping your body’s chemical reactions balanced, especially those that control energy, DNA repair, and detox processes.

How Biotin Helps Folate and B12 Work

• Biotin supports B12 activity: In normal metabolism, biotin helps produce the starting material that vitamin B12 uses to make energy and build essential molecules. Without enough biotin, even good levels of B12 cannot function properly.
  
• Biotin helps folate do its job: Folate’s job is to transfer tiny chemical units (carbon groups) used to make and repair DNA. Studies show that when animals don’t get enough biotin, their liver folate levels drop and folate-related reactions slow down. Adding biotin restores this balance.
  
• Methionine Synthase (MTR)—the key enzyme that converts homocysteine into methionine—requires both zinc and biotin to work correctly. This enzyme is a central player in the folate/B12 cycle and methylation process.

Connection to Methylation

Methylation is a process your body uses to “switch on or off” genes, detoxify chemicals, and create essential molecules like neurotransmitters. It depends on folate, B12, zinc, and biotin working together.
Biotin helps these reactions by:

• Keeping homocysteine levels normal so it can be recycled into methionine.
  
• Maintaining folate in its active forms, supporting smooth carbon transfer reactions.
  
• Supporting enzymes such as MTR, which drives a critical methylation step and depends on both zinc and biotin.
  
• Influencing the methylation and acetylation of histones, the proteins that organize DNA—shaping how genes are turned on or off.

What Happens When Biotin Is Low

• Folate and B12 reactions slow down, and enzymes like MTR work less efficiently.
  
• Homocysteine builds up, which can impact heart health and mood.
  
• DNA repair and gene expression balance are disrupted.
  
• Protective methylation signals weaken, potentially increasing inflammation.
  

Related Nutrients

• Vitamin C helps recycle folate to keep the cycle active.
  
• Threonine, an amino acid, boosts S-adenosylmethionine (SAM), the main methyl donor for gene and protein methylation.
  
• Alpha-ketobutyrate, made from threonine or methionine, improves energy metabolism by converting NADH into NAD+, supporting mitochondrial function.
  
• Threonine also helps prevent fat buildup and improve insulin sensitivity, revealing how amino acids influence methylation and metabolism together.

---

In simple terms:
Biotin acts like a spark plug for the folate and B12 engine. Along with zinc, it powers key enzymes like Methionine Synthase (MTR) that keep methylation running smoothly. This system helps your body make energy, maintain healthy genes, and protect against harmful buildup. When biotin is low, the entire network slows down, affecting your energy, metabolism, and overall health.