Early Infant Exposure to Excess Multivitamin: A Risk Factor for Autism?
Figure 2
Role of methyl groups and sulfur amino acids in the detoxification system. Methylation, sulfation, glutathione conjugation, and glutathione-mediated antioxidant defense are major components of the detoxification system. An adequate supply of methyl donors, primarily betaine and choline, is a prerequisite for methylation reactions. Glutathione, formed from cysteine, is required for glutathione conjugation and the clearance of hydrogen peroxide and hydroxyl radicals, while 3′-phosphoadenosine 5′-phosphosulfate (PAPS), derived from the metabolism of sulfur amino acids, is the universal sulfate donor for all sulfation processes. Excess vitamins may disturb the degradation of monoamine neurotransmitters by depleting the body’s methyl-group and sulfate pools. 1, methyltransferases; 2, glutathione S-transferase; 3, phase I xenobiotic-metabolizing enzymes; 4, glutathione peroxidases; 5, glutathione reductase; 6, sulfotransferases. 5-CH3-THF: 5-methyltetrahydrofolate; DMG: dimethylglycine; GSH: reduced glutathione; GSSG: oxidized glutathione; PAP: 3′-phosphoadenosine-5′-phosphate; R-OH: alcohols; ROOH: organic peroxides (which generate free radicals); THF: tetrahydrofolate.
