Cyclic fluctuations in arylphorin, the principal serum storage protein of Lymantria dispar, indicate multiple roles in development

Abstract

Arylphorin (Ap) was isolated and partially characterized from larval serum of the gypsy moth, Lymantria dispar (Lepidoptera: Lymantriidae). Non-denaturing and SDS-polyacrylamide gel electrophoresis suggest a 440,000 Da hexamer composed of nonidentical subunits of M r 73,000 and 80,000. Tyrosine and phenylalanine comprise 15.6% of the total protein amino acid. L. dispar Ap is immunologically related to Manduca sexta Ap. Hemolymph Ap concentrations throughout the larval stadia were determined using quantitative immunoelectrophoresis. Cyclic fluctuations in hemolymph concentrations are correlated with each molting cycle. A general increase in Ap concentration during each intermolt is followed by a sharp decline between apolysis and ecdysis. The last days of each instar were found to be the best time to sample protein titer with minimum variance. Hemolymph space, estimated by measuring the dilution of an injected foreign protein, is a constant 28% (v/w) of body weight. Total serum Ap per animal was calculated. A divergent allometric relationship between Ap accumulation and weight gain throughout the larval period results in the ultimate domination of the serum protein profile by Ap in the ultimate larval instar of the female in particular. An additional instar of Ap accumulation in the female gypsy moth is suggested to compensate for the lack of a predominantly female-specific storage protein in this species.