Phosphoinositides in the Flight Muscle of Periplaneta americana: Incorporation of Labelled Phosphate and Inositol

The content of phosphatidylinositol phosphate (DPI) in the flight musculature of the cockroach Periplaneta americana was found to be 30 nmol g ' wet weight, that of phosphatidylinositol-bis-phosphate (TPI) 6.5 nmol g wet weight. After administration of P-orthophosphate in vivo, the specific radioactiv­ ity (S.A.) of arginine phosphate reaches a plateau after 2 hours and remains constant for the subsequent 22 hours. The S.A. of all phospholipid phosphates except the phosphate in position 5 of TPI rises during this time. The diesteric phosphate of DPI and TPI has lower S.A. than the diesteric phosphate of phosphatidylinositol (PI) after 2, 6 and 24 hours of incorporation in vivo. The phosphates in position 4 of DPI and TPI incorporate with identical rate, the phosphate in position 5 of TPI incorporates very rapidly during the first 6 hours and after 24 hours its S.A. decreases only half the value found after 6 hours. After administration of 3 H-myo-inositol, the S.A. rises in all three phosphoinositides with identical rates.