title: Studies on avian erythrocyte metabolism. XII. The synthesis and degradation of inositol pentakis (dihydrogen phosphate).
abstract: The pathway(s) of synthesis and degradation of inositol 1, 3, 4, 5, 6 pentakis (dihydrogen phosphate) (inositol-P5), found predominantly in the avian erythrocyte, are unknown. Myo-inositol (inositol), D-glucose, inosine, and phosphate have been studied as potential precursors of inositol-P5 synthesis in chicken erythrocytes. Whole blood from chickens at several ages has been incubated for prolonged periods and the concentration of inositol-P5 measured to determine the ability of the avian erythrocyte to catabolize inositol-P5. Incubation of erythrocyte suspensions from 5-day chicks with [U-14 C]myo-inositol (inositol) for 17 hr lead to the appearance of 19.8% of the radioactivity in the aqueous acid-soluble extract of the erythrocytes (RBC). Fractionation of this extract on an anion exchange column yielded five major radioactive peaks, three of which represent 1) free myo-inositol, accounting for 63.5% of the radioactivity; 2) myo-inositol monokis (dihydrogen phosphate) (inositol-P), representing 1.6% of the radioactivity; and 3) inositol 1, 3, 4, 5, 6 pentakis (dihydrogen phosphate) (inositol-P5), representing 27.0% of the label in the erythrocyte. Sodium fluoride did not inhibit the incorporation of [U-14 C]myo-inositol into inositol-P5. Similar incubations with D-[U-14 C]-glucose and [U-14 C]-inosine yielded no incorporation of radioactivity into inositol-P5. These data are consistent with the interpretation that inositol is the major precursor for synthesis of inositol-P5 in chick red cells. Incubation of whole blood from 1-, 5-, and 42-day chicks and mature birds at 40 C for as long as 72 hr resulted in increases in RBC inorganic phosphate (Pi) thought due primarily to depletion of adenosine triphosphate (ATP). Inositol-P5 content of RBC of 5- and 42-day birds decreased 28 and 20%, respectively, after 72 hr, but no change was noted in inositol-P5 levels of RBC from mature birds. The red cells of the mature bird appear to be unable to catabolize inositol-P5 at significant rates. The apparent inability of the chicken erythrocyte to alter readily its concentration of inositol-P5 suggests that the hemoglobin oxygen delivery system of birds may be less adaptable to changing oxygen requirements by regulating the concentration of hemoglobin modulator than is that of the mammals.
mesh_terms: D000255:Adenosine Triphosphate / Q000097:blood; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002250:Carbon Radioisotopes; D002645:Chickens / Q000097:blood*; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D007288:Inosine / Q000097:blood; D007295:Inositol Phosphates / Q000096:biosynthesis* / Q000097:blood; D010710:Phosphates / Q000097:blood; D012969:Sodium Fluoride / Q000494:pharmacology; D013403:Sugar Phosphates / Q000096:biosynthesis*
chemical_list: D001786:Blood Glucose; D002250:Carbon Radioisotopes; D007295:Inositol Phosphates; D010710:Phosphates; D013403:Sugar Phosphates; C013571:inositol pentaphosphate; D007288:Inosine; D000255:Adenosine Triphosphate; D012969:Sodium Fluoride