Pyridoxal-5-phosphate (P-5-P) is the bioactive form of vitamin B6 found in our bodies.
What's it up to?
It is required for the synthesis of several neurotransmitters, including serotonin (for appetite, sleep, and mood), dopamine (involved in the regulation of blood pressure and heart rate), and GABA (a neurotransmitter that blocks impulses between nerve cells in the brain) (1, 2).
Though it is not a methyl donor like vitamin B9 (methylfolate) and B12 (methylcobalamin), P-5-P is necessary for homocysteine recycling (3). This is the change back into methionine using vitamin B12-related enzymes, keeping homocysteine lower. Elevated homocysteine levels affect the interior lining of blood vessels in the body or narrowing of blood vessels (4, 5).
(1) Hartvig, P., Lindner, K.J., Bjurling, P. et al. Pyridoxine effect on synthesis rate of serotonin in the monkey brain measured with positron emission tomography. J. Neural Transmission 102, 91–97 (1995).
(2) Vitamin B6: A Molecule for Human Health? Molecules 2010, 15(1), 442-459.
(3) Michelle C McKinley, Helene McNulty, Joseph McPartlin, JJ Strain, Kristina Pentieva, Mary Ward, Donald G Weir, John M Scott, Low-dose vitamin B-6 effectively lowers fasting plasma homocysteine in healthy elderly persons who are folate and riboflavin replete, The American Journal of Clinical Nutrition, Volume 73, Issue 4, April 2001, Pages 759–764.
(4) Effect of homocysteine-lowering therapy with folic acid, vitamin B12, and vitamin B6 on clinical outcome after percutaneous coronary intervention: the Swiss Heart study: a randomized controlled trial, JAMA, 2002 Aug 28;288(8):973-9.
(5) Homocysteine induces blood vessel global hypomethylation mediated by LOX-1, Genet. Mol. Res. 13 (2): 3787-3799 (2014).