HEMOLYMPH TITERS, CHROMOPHORE ASSOCIATION AND IMMUNOLOGICAL CROSS-REACTIVITY OF AN OMMOCHROME-BINDING PROTEIN FROM THE HEMOLYMPH OF THE TOBACCO HORNWORM, MANDUCA-SEXTA

A yellow-colored ommochrome-binding protein (OBP) isolated from the hemolymph of tobacco hornworm, Manduca sexta, appears to derive its color from ommatin D. Ommatin D is the sulfate ester of xanthommatin, the latter being an important metabolite of tryptophan in insects. The polypeptide chain of OBP was immunologically detected in the hemolymph at all stages of the life cycle. However, only during the fifth larval instar did OBP polypeptide levels in the hemolymph appreciate significantly. The highest OBP polypeptide concentration (approx. 0.45 mg/ml) was observed on the first day of pupation. Thereafter, the concentration of OBP polypeptide gradually decreased in pupal hemolymph. We found that association of chromophore with the OBP polypeptide was transient. In fifth instar wandering stage larvae and in female moths, OBP was detectable in the hemolymph. In feeding fifth instar larvae and in male moths, only apoOBP was detected (i.e. the OBP polypeptide without the chromophore). During-the wandering stage, increasing amounts of chromophore became associated with the OBP polypeptide. No representatives of seven other insect orders contained hemolymph proteins that cross-reacted with anti-OBP antiserum. However, when four other Lepidopteran species were examined, an immunologically-related hemolymph protein of approx. 31 kDa was detected in each animal. Whether these cross-reacting proteins also bind ommochromes remains to be investigated.