inosinic-acid and deoxyinosine

A cytosolic 5'-nucleotidase, acting preferentially on IMP and GMP, has been isolated from human colon carcinoma extracts. This enzyme activity catalyzes also the transfer of the phosphate group of 5'-nucleoside monophosphates (mainly, 5'-IMP, 5'-GMP, and their deoxycounterparts) to nucleosides (preferentially inosine and deoxyinosine, but also nucleoside analogs, such as 8-azaguanosine and 2',3'-dideoxyinosine). It has been proposed that the enzyme mechanism involves the formation of a phosphorylated enzyme as an intermediate which can transfer the phosphate group either to water or to the nucleoside. The enzyme is activated by some effectors, such as ATP and 2,3-diphosphoglycerate. Results indicate that the effect of these activators is mainly to favor the transfer of the phosphate of the phosphorylated intermediate to the nucleoside (i.e., the nucleoside phosphotransferase activity). This finding is in accordance with previous suggestions that cytosolic 5'-nucleotidase cannot be considered a pure catabolic enzyme.

Topics: 2,3-Diphosphoglycerate; 5'-Nucleotidase; Adenosine Triphosphate; Colonic Neoplasms; Cytosol; Diphosphoglyceric Acids; Guanosine Monophosphate; Humans; Inosine; Inosine Monophosphate; Kinetics; Phosphates; Phosphotransferases

Adenine nucleotide levels were measured in extracts of murine calvaria after different periods of culture with or without parathyroid hormone (PTH; 10(-8) M) or PGE2 (10(-7) M). In control calvaria the energy charge, (ATP + 1/2 ADP)/(ATP + ADP + AMP), remained at close to 0.7 over a 24 hour culture period. However, bones cultured with PTH or PGE2 showed a transient fall in the energy charge down to 0.5. This was not associated with a fall in total adenine nucleotides. The rate of adenosine metabolism in cultured bone in vitro was studied by determining the contents of adenosine, inosine, 2-deoxyadenosine, 2-deoxyinosine and hypoxanthine in the culture medium. There was a continuous increase in adenosine, inosine and hypoxanthine as well as a disappearance of medium 2-deoxyadenosine that was accounted for by appearance of 2-deoxyinosine. The deaminating activity could only partly be accounted for by activity in the medium and thus probably mainly resides in the bone cells. PTH (10(-8) M) did not alter the rate of disappearance of 2-deoxyadenosine or adenosine deaminase activity determined in bone extracts. The results demonstrate that two substances that increase calcium mobilization from bone alter ATP utilization and/or synthesis without significantly influencing adenosine production or metabolism.

Topics: Adenine Nucleotides; Adenosine; Adenosine Deaminase; Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Animals; Bone and Bones; Cells, Cultured; Deoxyadenosines; Dinoprostone; Hypoxanthine; Hypoxanthines; Inosine; Inosine Monophosphate; Mice; Parathyroid Hormone; Prostaglandins E; Uric Acid