Biochemical and Immunological Characterization of Ectopic Tumoral Renin

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Abstract
Biochemical and immunological characteristics of renin secreted by 2 [human] malignant renin-secreting tumors [pulmonary (PT) and paraovarian (POT)] were studied. They both contain inactive renin (IR), as renin activity of tumoral extracts was increased after acid activation or trypsin treatment (10.1-20.8 Goldblatt units/g tissue for PT and 1.4-3.71 for POT). Renin activity after activation reached the value obtained by direct RIA [radioimmunoassay] of human renin (23 and 3.4, respectively), as both forms are recognized by renin antiserum. Both enzymatic activities were completely inhibited by renin antiserum. Displacement curves for the 2 tumoral renins paralleled the MRC [Medical Research Council] renin in the direct RIA. After chromatography on affigel blue, active renin was not bound to the gel, and inactive renin eluted only with 1 M NaCl. On pepstatin A Sepharose and carboxybenzyl-pepstatin Sepharose (an N-modified-pepstatin), a separation of the 2 forms of pulmonary renin was obtained; inactive renin eluted with breakthrough proteins, whereas active renin was strongly bound to the gel. After this affinity chromatography, the MW of inactive and active renin, determined on Ultrogel, were very close (46,000 and 42,500). Ectopic renin in these cases is similar to the renal enzyme; renin can be secreted in an inactive form, supporting the hypothesis of an inactive initial state of renin; and MW differences between the 2 forms are very slight.