The concentrations of alanine, aspartate, glutamate, glutamine and serine plus threonine have been measured by enzymic methods in ;quick-frozen' livers from normal, starved, alloxan-diabetic and phlorrhizin-treated rats. 2. The hepatic concentrations of alanine and serine plus threonine were decreased in rats starved for 48hr. Treatment of these rats with phlorrhizin resulted in a rapid fall (within 2(1/2)hr.) in the concentrations of all the glucogenic amino acids except serine plus threonine, which increased. The pattern for alloxan-diabetic rats was similar to that for phlorrhizin-treated animals, except that here serine plus threonine also decreased in concentration. 3. The effects of anoxia on the hepatic concentrations of the glucogenic amino acids are reported. 4. Inhibition of glutamate-pyruvate transaminase in vivo by l-cycloserine resulted in the accumulation of alanine in situations involving high rates of gluconeogenesis from endogenous amino acids. 5. Measurements of the concentrations of the reactants of the glutamate-pyruvate transaminase and glutamate-oxoglutarate transaminase systems in various metabolic states suggest that they are both at or near equilibrium in rat liver. 6. New enzymic methods are described for the determination of serine plus threonine and alanine.
