Phosphorylations in rabbit liver in vivo

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Abstract
A time-course study was made of the distribution of tracer phosphate between plasma P and the acid-soluble P compounds of rabbit liver. Ion-exchange chromato-graphy was principal means of isolating the various P compounds. The removal of the tracer was found to follow the same biphasic exponential function as previously found in other mammalian species; the half-times of the 2 processes were found to be about 15 minutes and 3 hours. The slow process, which is considered to represent principally the exchange with the P compounds of the soft tissues, accounts for about 1/8 of the tracer removed from the plasma. Results suggest that there is a functional, if not a structural, "compartmentalization" of some of the acid-soluble P compounds within the cell, so that the entire quantity of some of them may not be equally available for turnover processes. Inorganic pyrophosphate was demonstrated to be present in the liver and to have a higher turnover rate than any of the intracellular organic P compounds, the results being consistent with the hypothesis that the formation of pyrophosphate on the cell membrane serves as a principal means for the entry of phosphate into the cell interior. Adenosine monophosphate (AMP) and uridine 5[image]-phosphate (UMP) may be formed by reactions at the cell membrane. The principal mechanism for the formation of adenosine diphosphate appears to be the reversal of the myokinase reaction. The concentrations of glucose 1-phosphate (G-1-P) and glucose 6-phosphate (G-6-P) in the liver were approximately equal, rather than with the G-6-P predominating, as required by the equilibrium of the phosphoglucomutase reaction. The specific radioactivity relations between G-l-P, G-6-P and P? of ATP indicate that G-6-P is formed by the phosphoglucomutase and hexokinase reactions taking place simultaneously. Data suggest a continuous cycling between blood glucose and liver glycogen whether or not there is net deposition of glycogen in the liver. The specific radioactivity relations of alpha glycerophosphate (GPA), phosphoglyceric acid (PGA) and P? of ATP suggest the oxidation of GPA rather than the glycolytic pathway as the principal means of formation of PGA. The turnover rate of fructose-1-phosphate was considerably lower than that of G-l-P. The turnover rate of UMP is considerably lower than that of AMP. Evidence suggests the principal means for the formation of AMP and UMP is the action of 5[image]-nucleotidase, operating in the direction of synthesis by coupling with oxidative reactions.