Key result
Acidification at 37°C irreversibly activated an inactive form of rabbit uterine renin, yielding an enzyme identical to active uterine renin.
This preclinical study demonstrates that inactive rabbit uterine renin can be acid-activated into a form identical to active renin, likely via proteolytic enzymes.
Hypothesis-generating in rabbits; leaves open whether acidification activates inactive uterine renin in humans.
Besides active renin an inactive form of renin could be demonstrated in uterine tissue. On gel filtration it was eluted as a molecule of slightly higher molecular weight than active renin, and it could be irreversibly activated by acidification at 37°C. The activation had a pH optimum between pH 3.8 and pH 5.3. Acid activated uterine renin was found identical to active uterine renin by 1) the formation of angiotensin I with time after addition of rat substrate, 2) the pressor response in the rat, 3) neutralization by antirenin and 4) similar Michaelian constants. Repeated freezing and thawing, acidification at 4°C and dialysis against 4 mol/l NaCl did not give any activation. A lower rate of activation of diluted samples and activation by trypsin at pH 7.4 suggest that proteolytic enzymes are involved in the activation.
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Jørgen Jørgensen (1979) studied this question. Acidification at 37°C vs. Acidification at 4°C, freezing/thawing, or dialysis was evaluated on Activation of inactive uterine renin. Acidification at 37°C irreversibly activated an inactive form of rabbit uterine renin, yielding an enzyme identical to active uterine renin.
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