Background: Silver is one of the heavy metals in environment and it,s amount in the earth shell is about 0.1 g per ton. Several studies have proven silver nitrate can produce ROS (oxygen reactive species) and harm cells through a variety of mechanisms including interactions with enzymes and proteins sulphydryl groups. Major sources of Silver in surface waters is natural leaching, human activities, such as mining, manufacture of silverware and jewellery, photografic manufacturing and processing which can elevate silver levels in aquatic environments.

Materials and Methods: In This study horseradish peroxidase (HRP) activity was determinded under steady-state kinetic conditions. Incubation of the enzyme with 1-100mM silver nitrate for 1-60 min in room temperature resulted in dual effects.

Results: Progressive inhibition of the enzymatic activity was observed after 30-60 min enzyme incubation with 0.05-100 mM of Ag+. After 30 and 60 min incubation time, enzyme inhibition was (35-60%) and (55-96%), respectively. However, in low concentrations of Ag+ (0.05mM ) and 15min incubation, reverse effects was observed and enzyme activity was increased up to 14/7μM/ s.

Conclusion: Results indicated that the effect of AgNo3 on HRP is time-and concentration- dependent.