Angiotensin-converting enzyme, although most prominent in vascular endothelium, has been identified in numerous tissues. Recent studies have indicated that several hormones, including glucocorticoids and thyroid hormone, may affect the activity of this enzyme. In the present study, angiotensin-converting enzyme was examined in homogenates of cultured human skin fibroblasts. Angiotensin-converting enzyme activity was measured by a radiometric assay using [Glycine-1-14C] Hippuryl-L-histidyl-L-leucine (1.1 mmol/L) as substrate, and was expressed as nmol hippuric acid formed per minute/mg protein. Angiotensin-converting enzyme was identified in all five cell strains tested, and the activity observed was 0.97 +/- 0.18 nmol/min/mg protein (mean +/- SE). The optimum pH was between 6.9 and 7.6, and optimum temperature was 37 degrees C, with loss of activity of 55 degrees C and higher. Buffer strength was optimized at Tris 0.025 mol/L, and 1.0 mol/L NaCl. Activity increased linearly with protein concentration and with time, and the Km = 1.14 mmol/L. The most potent inhibitor of fibroblast ACE was captopril (SQ 14,225) with an IC50 = 10(-10) mol/L; other inhibitors included SQ 20,881, EDTA, and phenanthroline. Competitive substrates included angiotensin-I, substance P, and bradykinin. Four hormones, T3 (10(-9)-10(-7) mol/L), 1,25 (OH)2D3 (10(-8)-10(-7) mol/L), dexamethasone (10(-7)-10(-6) mol/L), and a synthetic androgen, R1881 (10(-8)-10(-7) mol/L) were incubated with cells for 72 hours. In all incubations, there was no significant effect on cellular ACE activity induced by any agent. Angiotensin-converting enzyme activity in serum free media was less than 1% of cell activity and was unaltered by hormone treatment.(ABSTRACT TRUNCATED AT 250 WORDS)