A NOVEL CALCIUM-INDEPENDENT ENZYME CAPABLE OF INCORPORATING PUTRESCINE INTO PROTEINS

A Ca++-independent enzyme capable of incorporating [H-3]-putrescine in to proteins was detected in the rat intestine mucosa. The Ca++-indepen dent incorporation of [H-3]-putrescine into proteins was temperature-, pH-, time-, and dose-dependent. However, this enzyme was absent in th e gastric mucosa. Similar to testicular Ca++-dependent transglutaminas e, the optimal pH of intestinal Ca++-independent enzyme was 9.0. At 10 (-5) M or less putrescine concentrations, the Ca++-independent enzyme in an intestinal cytosol preparation showed a greater activity than di d the Ca++-dependent transglutaminase. However, at higher putrescine c oncentrations, the latter showed a greater activity than did the forme r. Both the intestinal Ca++-dependent and independent enzymes were inh ibited by cystamine, thermal labile at 50 degrees C and precipitated b y 30 to 50% saturation of ammonium sulfate. The fact that these two en zymes shared many similar characteristics, with the exceptions of Ca+-requirement, suggests that they may have similar active site and intr insic molecular function(s). (C) 1998 Academic Press.