PROPERTIES AND SIGNIFICANCE OF A RIBOFLAVIN-BINDING HEXAMERIN IN THE HEMOLYMPH OF HYALOPHORA-CECROPIA

Citation
J. Magee et al., PROPERTIES AND SIGNIFICANCE OF A RIBOFLAVIN-BINDING HEXAMERIN IN THE HEMOLYMPH OF HYALOPHORA-CECROPIA, Archives of insect biochemistry and physiology, 25(2), 1994, pp. 137-157
Citations number
33
Categorie Soggetti
Entomology,Biology,Physiology
ISSN journal
07394462
Volume
25
Issue
2
Year of publication
1994
Pages
137 - 157
Database
ISI
SICI code
0739-4462(1994)25:2<137:PASOAR>2.0.ZU;2-N
Abstract
A riboflavin-binding hexamerin isolated from pupal hemolymph of Hyalop hora cecropia has a native M(r) of 510,000, subunit M(r) of 85,000, an d a 5% carbohydrate content. An intrachain cross-link was confirmed in protease limit digests. Ellman titration confirmed the presence of a sulfhydryl group, which is needed for this linkage. Though CU2+ is kno wn to promote the linkage, heavy metals were not detected in the isola te. Heat denaturation released ligand with the absorbency, fluorescenc e spectra, and chromatographic behavior of riboflavin. Binding resulte d in substantial quenching of the fluorescence of both the isoalloxazi ne in riboflavin and of aromatic groups in the apoprotein. Kinetic ana lysis indicated a K-D of 2.5x (-7) M for riboflavin, 1.3 x 10(-7) M fo r lumiflavin, and greater than 1 x 10(-6) M for 10 FMN and FAD. Over f our moles of flavin were bound per mole of hexamerin. The amount of ri boflavin in pupal hemolymph is sufficient to occupy only 2-3 of these sites. Riboflavin is also associated with lipophorin and vitellogenin, but the molar ratios after protein isolation were low. On a standard laboratory diet, riboflavin is in great excess, but most of it is appa rently excreted before the apoprotein first appears in the hemolymph, just before wandering. The concentration of riboflavin-binding hexamer in rises to 15-30 mg/ml in pupae; relative to other hexamerins, very l ittle is stored in the fat body. All of the apoprotein and 75% of ribo flavin disappear from the hemolymph during adult development. An amoun t of flavin at least equal to that stored in pupal hemolymph is transf erred to the eggs formed during this period. (C) 1994 Wiley-Liss, Inc.