[Effect of prosthetic group of horseradish peroxidase on enzyme stability].

Constants of inactivation rate of horseradish peroxidase (HRP) apo-HRP and apo-HRP-protoporphyrin (PP) are estimated at the pH range 2.8-12.8 and 25 degrees C. Two ionogenic groups (acid and alkaline) are detected on cases of HRP and apo-HRP, which are responsible for stable HRP conformation. HRP stability within the pH range 5-10 exceeded 30 times that of apo-HRP, while the stability apo-HRP-PP complex is similar to that of apo-HRP. The data obtained show that formation of complex of apo-HRP with PP, an analogue of the prostetic group lacking central Fe atom, practically does not affect the stability of HRP protein globula at pH 5-10, but significantly stabylized apo-HRP at the extreme pH values. The complex formation of apo-HRP with active prosthetic group - hemin - results on the stable conformation of the HRP protein globula, which suggests a determining role of Fe ion - porphyrin complex (hemin) on the support of the stable HRP structure.