PMID: 7012149May 10, 1981Paper

Structural proteins of sarcophagid larval exoskeleton. Composition and distribution of radioactivity derived from [7-14C]dopamine.

The Journal of Biological Chemistry
H LipkeM Sugumaran

Abstract

In the cyclorrhaphid flies, exoskeletal proteins from the last larval instar cross-link by arylation and glycosylation to form the sclerotized puparial case. Cuticular proteins from maggots killed just prior to tanning were resolved into 21 soluble components by isoelectric focusing and sodium dodecyl sulfate-polyacrylamide electrophoresis. Isoelectric points ranged from pH 4.5 to 6.0, molecular weights were distributed between Mr = 16,000 and 24,000. Aspartic and glutamic acids, glycine, serine, valine, and lysine were abundant in all the proteins while sulfur-containing residues were uniformly absent. Heterogeneity was manifest among NH2 termini of the soluble fractions, while the insoluble chitin-linked protein showed only aspartic acid in this position. The sclerotized matrix was assembled by a concerted bridging of protomers without accumulation of di-, tri-, or higher n-mers in the urea-soluble fraction. This mechanism was also favored by uniform distribution of the bridge precursor, [7-14C]dopamine, among the individual larval protomers including the polypeptide bound to chitin. Following administration of isotopic catecholamine 2 to 10 h prior to sclerotization, unbridged larval cuticle retained 3% of the radioactivity,...Continue Reading

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