inosinic-acid and malic-acid

Formation of adenine nucleotides, IMP, malate + fumarate, ammonia, adenosine, and inosine + hypoxanthine + uric acid were measured in cytosolic extracts from renal cortex and medulla. The order of substrate addition was IMP, then 2-deoxyglucose, then P-creatine. Compared with cortex, medulla showed greater rates of formation of adenosine triphosphate (ATP) from P-creatine, of adenosine monophosphate (AMP) from 2-deoxyglucose, and of total adenine nucleotides from IMP. These results suggest that the purine nucleotide cycle is more active in medulla than in cortex. This cycle may provide a mechanism in medulla for storing purine nucleotides which can be used to restore ATP pools in the relatively hypoxic conditions of this part of the kidney.

Topics: Adenosine Monophosphate; Adenosine Triphosphate; Animals; Aspartic Acid; Cytosol; Fumarates; In Vitro Techniques; Inosine Monophosphate; Kidney Cortex; Kidney Medulla; Malates; Purine Nucleotides; Rats; Rats, Inbred Strains

Experimental results on fast-twitch muscle of rainbow trout following exercise and during subsequent recovery lead us to a reinterpretation for the function of the components of the purine nucleotide cycle (PNC). Exhaustive exercise depletes tissue ATP by more than 90% and results in a stoichiometric gain in IMP and ammonium ions. Simultaneously, white-muscle aspartate decreases by half, but its maximum contribution can account for less than 2% of the accumulated ammonium. Of the three enzymes of the purine nucleotide cycle, AMP deaminase, adenylosuccinate synthetase and adenylosuccinate lyase, only AMP deaminase is functional during exhaustive exercise. During the slow (greater than 15 hour) recovery, AMP deaminase is effectively shut off, while the other two enzymes replenish the adenylate pool. At all times, a tight inverse correlation exists between ATP and IMP concentrations. Tissue ammonium and malate supply the required aspartate. Theoretical treatment with special attention to proton dynamics in a potentially anaerobic tissue also leads to the conclusion that rather than constituting a true cycle, distinct parts of the PNC are temporally segregated. We hypothesize that during periods of high energy demand, exclusively AMP deaminase is activated as a means (1) to push the myokinase reaction toward ATP synthesis, (2) to supply allosteric effectors, and (3) to remove some of the accumulating protons through the formation of ammonium, all at the expense of the adenylate pool. The process leading to its replenishment, which involves the production of two protons and the consumption of a high-energy phosphate, can be active during aerobic recovery only.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adenosine Monophosphate; Adenosine Triphosphate; Ammonia; Animals; Aspartic Acid; Inosine Monophosphate; Malates; Models, Biological; Physical Exertion; Purine Nucleotides; Reference Values; Salmonidae; Trout