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Biomedical subjects

E J Carlson

Publications and source records attributed to E J Carlson.

59 records · Page 4Linked to original sources
PubMed1978

Big renin in plasma of healthy subjects on high sodium intake.

Normal human plasma contains not only active renin but also an inactive form of renin which, after exposure to low pH, can generate angiotensin I from renin substrate. When healthy volunteers were given first a diet containing 400 mmol sodium and then a diet containing 10 mmol sodium for 4 days the changes in salt intake stimulated large changes in active plasma-renin and smaller changes in inactive renin. Inactive renin comprises a larger fraction of total renin in plasma of salt-loaded healthy subjects than salt depleted subjects. When plasma of healthy men on a high-salt diet was applied to a column of 'Sephadex G-100', renin eluted in two peaks, corresponding to big renin (60 000 daltons) and normal renin of lower molecular weight (40 000 daltons). Active and inactive forms of renin were present in both peaks. Plasma from salt depleted healthy subjects showed a large single peak of renin activity with a maximum at 40 000 daltons. These studies demonstrate that both big and small renin can exist as inactive or active enzyme. Big renin, previously found in certain diseases and in pregnancy, is also present in normal human plasma. These observations suggest a possible physiological role for big renin.

Chromatography, Gel↗
PubMedDate not supplied

Inactive renin of high molecular weight (big renin) in normal human plasma. Activation by pepsin, trypsin, or dialysis to pH 3.3 and 7.5.

Normal plasma contains inactive renin, which becomes active when plasma is dialyzed to pH 3.3 and to pH 7.5, or treated with pepsin or trypsin. Under optimal conditions, each of these procedures activated the same quantity of renin, which was not further increased by repeating or combining two procedures, thus suggesting that the same pool of inactive renin was activated by each procedure. When plasma was fractionated by gel filtration, dialysis activated very little renin in eluates. Trypsin activated renin, but under some conditions also destroyed renin. Pepsin fully activated the inactive renin in eluates without evidence of destruction of renin. The pepsin-activated renin of normal plasma eluted from Sephadex G-100 in a peak of apparent molecular weight (MW) 58,000 and from Sephacryl S-200 with apparent MW 53,000, like big renin in plasma of patients with diabetic nephropathy. Inactive renin was usually increased in amount in plasma of sodium-depleted normal men, but the elution volume did not change with sodium intake. When renin was fully activated in plasma incubated with pepsin or trypsin, the apparent MW of the main peak of big renin did not change appreciably. Inactive renin in plasma was usually increased after sodium depletion, but the elution volume did not change. Active renin of normal plasma had an apparent MW near 41,000 on both gels. Thus, we conclude that big renin is present in normal plasma in amounts at least equal to and usually greater than active renin (the ratio depending on sodium intake) and that pepsin activation readily demonstrates big renin in eluates from gel filtration.

Adult↗
PubMedDate not supplied

Mechanism of acid-activation of renin: role of kallikrein in renin activation.

Dialysis of plasma in pH 3.3 and then pH 7.5 is a method commonly used to activate plasma inactive renin. Endogenous plasma kallikrein has been shown to participate in activation during neutral dialysis. The present studies demonstrate that plasma inactive renin is fully activated following dialysis to pH 3.3 at 10 degrees C. Activation by low pH is a reversible process when followed by titration to a pH greater than 4.0. The rate of reversal of acid activation increases with increasing pH and temperature, reaching a maximum at pH 7.0 ad 37 degrees C. the disappearance of activated renin is not due to its destruction, because dialysis back to pH 3.3 fully restores activation. A preparation of renin zymogen devoid of active renin also shows complete reversal of activation. The Km of acid-activated renin is the same as that of endogenous active renin. Acid-activated renin (untreated by protease) elutes with an apparently greater Stokes radius than non-acid-treated inactive renin on Sephadex G-100. Once reversal of acid activation occurs, renal or plasma kallikrein has no effect on renin. However, once kallikrein acts on acid-activated renin, activation is no longer reversible. These data can explain the mechanism of acid activation of renin and the contribution of plasma kallikrein to renin activation in vitro. At low pH, inactive renin appears to undergo a conformational change such that the active site is accessible. Acid may unfold the renin molecule, as suggested by an increase in Stokes radius following acid dialysis. Kallikrein may then cleave a small peptide that permanently maintains acid-activated renin in an active state. Thus, renin zymogen must be in an active conformation such as that induced by acid to be "acted upon" by kallikrein, suggesting that other factors, in addition to renal kallikrein, may be involved in renin activation in vivo.

Acids↗