Synthesis of carbamoyl phosphate by carbamoyl phosphate synthetase I in the absence of acetylglutamate. Activation of the enzyme by cryoprotectants

Abstract

Glycerol, dimethylsulphoxide, ethylene glycol and sucrose but not polyethyleneglycol or bovine serum albumen, activate rat liver carbamoyl phosphate synthetase I in the absence of the cofactor acetylglutamate. Maximum activation is seen at 7–8 M-OH groups or at 1.6 M dimethylsulphoxide. The reaction has the normal stoichiometry and the partial reactions of ATP hydrolysis and ATP synthesis are also stimulated. Activation by such diverse agents strongly supports a purely allosteric role for acetylglutamate in the enzyme reaction. The importance of cryoprotectants present in studies on carbamoyl phosphate synthetases is discussed.