... masses of %25 and % 28 kDa. In the pres-ence of ATP and UTP (10 mMeach) (B), and CTP (2.5 mM)(C),onlyproduction of the 10- and 53-kDa cleavage fragments is observed. Inthe presence of GTP ... inactivation of wild-type CTPS by trypsin. (A)Inactivation of CTPS-catalysed NH3-dependent CTP formation in theabsence of ligands (s) and in the presence of ATP (10 mM, n), UTP(10 mM, h),andATPandUTPcombined(10mMeach, ... of the time of incubation. The ability of variousligands to protect both wild-type and mutant CTPS fromproteolysis was examined using ATP (0.5, 1.0, 2.0, and 10 mM), UTP (0.5, 1.0, 2.0, and...