Totally inactive renin zymogen and different forms of active renin in hog brain tissues

The nature of the activable form of renin in the kidney and other tissues has not been clear. Its identification and isolation from kidney have been hampered by rapid activation due to high levels of proteases. Using a pepstatin-Sepharose column, which distinguishes inactive renin from the active enzyme, evidence was obtained for the presence of a totally inactive zymogenic precursor of renin in the pituitary, pineal, and other regions of hog brain. The precursor has an approximate molecular weight of 50,000 and conversion to the active enzyme causes reduction in molecular weight to 43,000. Conversion of this active enzyme to an active but high molecular weight form (60,000) was also observed when the pituitary extract was treated with thiol-blocking reagents. This result was interpreted to indicate the presence of a binding protein. This study has demonstrated that inactive renin zymogen is different from so-called active big renin, which is a complex of active renin and the binding protein.