Photochemical evidence for the presence of histidyl residue in the active site of alkaline mesentericopeptidase.
The photosensitized oxidation of alkaline mesentericopeptidase in the presence of methylene blue results in a first-order rate of inactivation. The loss of enzymatic activity towards casein and N-acetyl-L-tyrosine ethyl ester closely correlates with the destruction of one histidyl residue. A pK value of 6.8 is determined from the sigmoid pH-dependence of the photoinactivation rate. This suggests the involvement of a normal titrating imidazole group in the active site of mesentericopeptidase. The competitive inhibitor Na-benzoyl-L-arginine protects the enzyme from photoinactivation. A conclusion is made that the active site histidyl residue is modified. Circular dichroism spectra show no change in the protein conformation during the photodynamic treatment.
Photochemical evidence for the presence of histidyl residue in the active site of alkaline mesentericopeptidase. The photosensitized oxidation of alkaline mesentericopeptidase in the presence of methylene blue results in a first-order rate of inactivation. The loss of enzymatic activity towards casein and N-acetyl-L-tyrosine ethyl ester closely correlates with the destruction of one histidyl residue. A pK value of 6.8 is determined from the sigmoid pH-dependence of the photoinactivation rate. This suggests the involvement of a normal titrating imidazole group in the active site of mesentericopeptidase. The competitive inhibitor Na-benzoyl-L-arginine protects the enzyme from photoinactivation. A conclusion is made that the active site histidyl residue is modified. Circular dichroism spectra show no change in the protein conformation during the photodynamic treatment.