CARBOXYDIPEPTIDASE FROM BOOPHILUS-MICROPLUS - A CONCEALED ANTIGEN WITH SIMILARITY TO ANGIOTENSIN-CONVERTING ENZYME

A protein, Bm91, which was first identified as a protective vaccine antigen from the tick Boophilus microplus, has regions of very strong amino acid sequence similarity to mammalian carboxydipeptidases or angiotensin converting enzymes (ACE; E.C. 3.4.15.1), This protein is now shown to share many biochemical and enzymatic properties with mammalian carboxydipeptidases, It is enzymatically active in a conventional assay for ACE using hippuryl-Gly-Gly as substrate, The hydrolysis of the C-terminal nonapeptide of the insulin B chain proceeds by sequential removal of carboxy-terminal dipeptides. The similarities extend to the dependence of activity on pH and added salt, Bm91 is inhibited by two well-characterized inhibitors of the mammalian enzymes, the drug Captopril and a nonapeptide, and the inhibition occurs in similar concentration ranges to those effective with the mammalian enzymes, However, the natural substrates of the tick enzyme are unknown, Angiotensin I itself is a poor substrate and the enzyme's natural substrates are likely to be one or more of the pharmacologically active peptides occurring in insects and arthropods.