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

A protein, Bm91, which was first identified as a protective vaccine an tigen from the tick Boophilus microplus, has regions of very strong am ino acid sequence similarity to mammalian carboxydipeptidases or angio tensin converting enzymes (ACE; E.C. 3.4.15.1), This protein is now sh own to share many biochemical and enzymatic properties with mammalian carboxydipeptidases, It is enzymatically active in a conventional assa y for ACE using hippuryl-Gly-Gly as substrate, The hydrolysis of the C -terminal nonapeptide of the insulin B chain proceeds by sequential re moval of carboxy-terminal dipeptides. The similarities extend to the d ependence of activity on pH and added salt, Bm91 is inhibited by two w ell-characterized inhibitors of the mammalian enzymes, the drug Captop ril and a nonapeptide, and the inhibition occurs in similar concentrat ion ranges to those effective with the mammalian enzymes, However, the natural substrates of the tick enzyme are unknown, Angiotensin I itse lf is a poor substrate and the enzyme's natural substrates are likely to be one or more of the pharmacologically active peptides occurring i n insects and arthropods.