How important is MAT1A in the SAM/methionine story?Updated 4 months ago

There are several isoforms of MAT (MAT1aI/III) and MAT2a and there is a complicated switching mechanism back and forth for them depending on the nutritional status at any given moment. In low methionine/fasting conditions both BHMT and MAT1aI/III get up-regulated in the liver. MAT1a also up-regulates in the intestines in effort to capture any methionine making its way thru the GI tract. The activation of this portion of the methionine cycle during starvation may serve as a mechanism to preserve the SAM pool for methylation reactions and to hoard methionine during nutrient deprivation. Then, once fed, the switch flips and BHMT/MAT activity slows down in the liver and the methionine and amino acid pool can participate in other necessary pathways needed by the body (transsulfuration, biosynthesis of phospholipids, creatine, and polyamines).