Cloning and expression of a novel juvenile hormone-metabolizing epoxide hydrolase during larval-pupal metamorphosis of the cabbage looper, Trichoplusia ni

A full‐length cDNA encoding for a microsomal juvenile hormone (JH)‐metabolizing epoxide hydrolase (TmEH‐1) was isolated from a cDNA library constructed from fat body of last stadium (wandering) cabbage loopers, Trichoplusia ni, at the exact developmental time of maximum JH epoxide hydrolase activity. TmEH‐1 was 1887 base pairs in lenght with a 1389 base pair open reading frame encoding 463 amino acids. Amino acid sequence analysis showed that TmEH‐1 was most similar to and contained the exact catalytic triad (Asp‐226, Glu‐403 and His‐430) found in microsomal epoxide hydrolases. TmEH‐1‐specific message was present along with JH III epoxide hydrolase activity in fat body in feeding (days 1 and 2) and wandering (day 3) larvae with the peak in message level preceding the peak in JH epoxide hydrolase activity by 1 day. When TmEH‐1 was expressed in baculovirus‐infected Spodoptera frugiperda cells, a 46,000 molecular weight protein appeared on SDS‐PAGE which corresponded to the predicted size coded by the TmEH‐1 message and which was positively correlated with increases in JH III epoxide hydrolase activity above that of wild‐type controls. In subcellular distribution studies, 58% of the juvenile hormone III epoxide hydrolase activity was in the insoluble fractions. Baculovirus expressed TmEH‐1 demonstrated a higher specific activity for JH III as compared to the general EH substrates, cis‐ and trans‐stibene oxide. Southern blot analyses suggested that multiple epoxide hydrolase genes are present in T. ni.