The Stability of the glutathione pools in the face of input fluctuations. Panel A shows the amino acid input to the model hepatocytes throughout a 24 hour day. The input is 25% of the mean while fasting, 175% of the mean for three hours after breakfast and lunch, and 325% of the mean for three hours after dinner. For discussion, see the text. Panel B shows moderate variations in methionine concentrations and extremely large swings in SAM concentration, but GSH concentration remains stable. Panel C shows that the velocity of the CBS reaction varies dramatically, but the velocity of the GS reaction, which synthesizes glutathione, shows milder variation. As expected, the long range allosteric reactions between the folate cycle and the methionine cycle stabilize the velocity of the DNA methylation reaction (vDNMT). Panel D shows that there are large variations in 5mTHF and Hcy throughout the day, but the GSH concentration in the blood remains stable.