Effects of calcium and limited proteolysis on membrane‐bound and releasable dopamine β‐hydroxylase in adrenomedullary catecholamine granules

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Abstract
HELLE, K.B., PIHL, K.E. & SERCK-HANSSEN, G. 1985. Effects of calcium and limited proteolysis of membrane-bound and releasable dopamine β-hydroxylase in adrenomedullary catecholamine granules. Acta Physiol Scand125, 423–427. Received 9 January, accepted 6 May 1985. ISSN 0001–6772. Department of Physiology, University of Bergen, Norway. Bovine chromaffin granules were shown to contain two potent proteolytic systems resulting in limited proteolysis of granule proteins at pH 6.0 in the cold in the presence of inhibitors of serine and thiol proteases. Calcium, whether added during lysis or remaining bound to the lysate protein during dialysis in non-chelating solutions, enhanced recoveries of total immunoreactive dopamine β-hydroxylase (14% of total protein) and soluble enzyme (9% of lysate protein) due to degradation of chromogranins. A pepstatin A-blockable, catepsin D-like proteolytic system converting membrane-bound enzyme to its soluble counterpart at pH 6.0 was detected in the granule membrane fraction.