A membrane-associated form of L-DOPA decarboxylase in the white prepuparium and adult eclosion developmental stages of the Mediterranean fruit fly, Ceratitis capitata

Abstract

L-DOPA decarboxylase (DDC: EC 4.1.1.28) has been extensively studied in both mammals and insects. DDC is generally considered to be a cytosolic enzyme. This work, however, presents evidence on the association of DDC molecules with the membranes of the white prepuparium and adult eclosion developmental stages of Ceratitis capitata (Mediterranean fruit fly). Membrane-associated DDC immunoreactivity and enzymatic activity was detected by immunoblotting using polyclonal antisera and enzymatic assay experiments. Fractionation of membranes by temperature-induced phase separation in Triton X-114 resulted in the recovery of membrane-associated DDC activity in separation phases where integral and hydrophobic membrane proteins separate. Treatment of membranes with phosphatidylinositol-specific phospholipase C, was not sufficient to remove membrane-associated DDC activity, further suggesting that a population of DDC molecules exists embedded within membranes. In light of the recent evidence describing DDC as a regulated enzyme, a study of the functional significance of the enzyme's association with membranes may provide us with new clues about the biological pathways that this molecule is involved in.