A role of the "handle" region in the prorenin prosegment sequence was investigated to demonstrate the crucial non-proteolytic activation of prorenin by binding to the recombinant (pro)renin receptor on the COS-7 cell membrane. The plasmid DNA containing either rat or human (pro)renin receptor was transfected into the COS-7 cells. The highest amount of receptor was observed on the COS-7 cell membrane after 18 h transfection. Of the total rat and human prorenin, 90% and 50% were bound to each of the respective receptors, respectively. The Kd values were 0.89 and 1.8 nM, respectively. Rat prorenin was activated non-proteolytically by the receptor. The Km was determined 1.0 microM when sheep angiotensinogen was used as the substrate. Human prorenin was also activated by the receptor. The Km was 0.71 microM. Additionally, decapeptides (10P-19P) known as "decoy" peptide and pentapeptides (11P-15P) named "handle" region peptide, were observed to inhibit the binding of both prorenins to receptors, respectively. The Ki were similar around 7 nM for both the peptides. Other two region peptides in the prosegment did not interfere the binding. These results show that the "handle" region probably plays a crucial role in prorenin binding to the receptor and in its enzymic activity by non-proteolytic activation.