Abstract
Cleavage of prorenin's prosegment causes irreversible formation of renin. In contrast, renin activity is reversibly exposed when prorenin is acidified to pH 3.3. Nonetheless, acidification of plasma results in irreversible activation of prorenin, because endogenous proteases cleave the prosegment of acid-activated prorenin. Chilling of plasma results in irreversible cryoactivation of prorenin. In this study we investigated whether cryoactivation of purified prorenin is reversible. The intrinsic renin activity of recombinant human prorenin was measured by an enzyme kinetic assay using partially purified human angiotensinogen as substrate. Results are expressed as a percent (mean +/- S.E.) of the maximal activity exposed after limited proteolysis by trypsin. The intrinsic renin activity of two pools (0.3 and 0.06 Goldblatt units/ml) was 1.5% +/- 0.3 and 1.2% +/- 0.6 at 37 degrees C. Activity increased to 19% +/- 0.3 and 26% +/- 0.5 after incubation at 0 degrees C and to 5.4% +/- 0.5 and 2.1% +/- 1.2 at room temperature. Cryoactivation did not occur in buffers containing more than 1 M NaCl. It took 8 min at 37 degrees C or 180 min at room temperature for cryoactivated prorenin to lose half of its intrinsic renin activity. It took 48 and 26 h, respectively, at 0 degree C for the two pools of prorenin at 37 degrees C to regain half of their maximum intrinsic activity at 0 degrees C. A direct immunoradiometric assay that detects active renin but not prorenin was able to detect cryoactivated prorenin. These results show that human prorenin can be reversibly cryoactivated in buffers of low ionic strength and has greater intrinsic activity at room temperature than at 37 degrees C.
Highlights
Cleavage of prorenin's prosegment causes irrevers- inant butnot the only source of circulating prorenin
The intrinsic renin activity of recombinant human prorenin was measured by an enzyme kinetic assay using partially purified humaanngiotensinogen as substrate
Results are expressed asa percent of the maximal activity exposed after limited proteolbut ovarian prorenin secretion is regulated by luteinizing hormone and human chorionic gonadotropin [11].For example plasma prorenin increases 2-fold at ovulation and 10-fold during pregnancy [15]
Summary
Cleavage of prorenin's prosegment causes irrevers- inant butnot the only source of circulating prorenin. Renin activity is adrenal cortex, and female reproductive organs are examples reversibly exposed when prorenin is acidified to pH of extra-renal sources of prorenin [9,10,11,12,13]. Reversible activation of prorenin, because endogenous Prorenin may have a regulated function. The intrinsic renin activity of recombinant human prorenin was measured by an enzyme kinetic assay using partially purified humaanngiotensinogen as substrate. Results are expressed asa percent (mean f S.E.) of the maximal activity exposed after limited proteolbut ovarian prorenin secretion is regulated by luteinizing hormone and human chorionic gonadotropin [11].For example plasma prorenin increases 2-fold at ovulation and 10-fold during pregnancy [15].
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