[Spectrophotometric assay of angiotensin I-converting enzyme (author's transl)]

The method of chemical assay of angiotensin I-converting enzyme described is a modification of the previously published spectrophotometric assay based on quantitation of hippuric acid released from hippuryl-L-histidyl-L-leucine. The new procedure involves extraction of hippuric acid with ethylacetate, evaporation to dryness of the extract, solubilization of the residue with 1 mol/l NaCl and purification with petroleum ether before measurements of the absorbance at 228 nm of the aqueous phase. Under these conditions, hippuric acid insoluble in petroleum ether remains in the aqueous phase, whereas other A228-absorbing materials, readily soluble in the ether and able to interfere with the assay, are eliminated.