Biochemistry - Chemical Reactions in Living Cells, Volume 2 - D. Metzler 1980

Biosynthesis: How New Molecules Are Formed
Regulation of Biosynthetic Processes
Gluconeogenesis

When a large amount of lactate reaches the Liver, it is oxidized to Pyruvate, which then enters the Cell/35.html">Mitochondria. Here, a portion of it enters The Tricarboxylic Acid Cycle and undergoes oxidation. However, if the ATP concentration is high, pyruvate dehydrogenase is inhibited (Chapter 9, Section B, 4). In this case, The amount of pyruvate converted into oxaloacetate and malate [Equation (9-9)] may increase. Malate can leave the mitochondrion to be re-oxidized to oxaloacetate, which serves as a precursor for PEP and Glycogen synthesis (bold dashed arrows in Fig. 11-11). When the ATP concentration is high, Phosphofructokinase is inhibited, whereas a specific phosphatase (fructose-1,6-diphosphatase), which catalytically removes a single phosphate group from fructose diphosphate [Equation (11-19), step d], remains active. If Blood glucose levels are low, glucose-6-phosphate in the liver is hydrolyzed by another specific phosphatase—glucose-6-phosphatase (localized in The Endoplasmic reticulum)—yielding free glucose. The greater part of the glucose-6-phosphate, however, is converted into glycogen. In Skeletal Muscle, glucose-6-phosphate is almost entirely absent, and under normal conditions, Muscle tissue is unable to release free glucose.

Hepatic Gluconeogenesis is significantly stimulated by Glucagon and epinephrine. The effects mediated by cyclic AMP may include The stimulation of fructose-1,6-diphosphatase and the inhibition of phosphofructokinase [46]. The influence on the interplay between pyruvate and PEP, which also occurs, may be indirect, involving the stimulation of α-ketoglutarate METABOLISM.