IDENTIFICATION OF AN ANNEXIN-LIKE PROTEIN AND ITS POSSIBLE ROLE IN THE APLYSIA EYE CIRCADIAN SYSTEM

Light and serotonin regulate the phase of the circadian rhythm of the isolated eye of Aplysia. To screen for possible protein components of the eye circadian oscillator, we identified a number of proteins whose synthesis was altered in opposite ways by light and serotonin. The ce llular function of one of these proteins was investigated by obtaining a partial amino acid sequence of it and by examining its immunoreacti vity. A 38-amino acid sequence was obtained from a 40-kDa (isoelectric point 5.6) protein. A greater than 60% amino acid identity existed be tween this sequence and sequences of a family of calcium/phospholipid- binding proteins called annexins. Furthermore, the 40-kDa protein reac ted with antibodies generated against a conserved amino acid sequence of annexins and with antibodies raised against human annexin 1. The id entification of the 40-kDa, light- and serotonin-regulated protein as an annexin led us to hypothesize that arachidonic acid metabolism play s a role in the Aplysia eye circadian system. To test this hypothesis, we examined the ability of an inhibitor of the arachidonic acid metab olic pathway to perturb the eye rhythm. Pulse treatments of isolated e yes with a lipoxygenase inhibitor, nordihydroguaiaretic acid, phase sh ifted the rhythm. The phase-shifting ability of nordihydroguaiaretic a cid suggests that arachidonic acid and some of its metabolites may pla y a role in the eye circadian system. The results of our studies raise the possibility that links may exist between the 40-kDa annexin-like protein, arachidonic acid metabolism, and the circadian oscillator.