TAURINE METABOLISM IN LARVAE OF MARINE MOLLUSKS (BIVALVIA, GASTROPODA)

Nonfeeding larvae of the gastropod Haliotis rufescens maintained a con stant amount of taurine during embryonic and larval development and, s ince no de novo synthesis of taurine was observed in these larvae, the maternal endowment of taurine to the egg was sufficient for larval de velopment to metamorphosis, In contrast, feeding larvae of the bivalve Crassostrea gigas increased their taurine content by a factor of 43 d uring growth to metamorphosis (from 86 to 311 mu m, valve length). Tau rine was not present in algae used to feed the larvae, suggesting that de novo synthesis of taurine by the larvae met their requirements, In unfed larvae, cysteic acid, cysteine sulfinic acid and hypotaurine we re labeled from a [S-35]cysteine precursor, but taurine was not, Hyper osmotic treatment (from 33 parts per thousand to 44 parts per thousand salinity for up to 3h) did not induce taurine synthesis in unfed larv ae, However, larvae fed the alga Isochrysis galbana up-regulated their taurine synthesis from [S-35]cysteine by a factor of 11 (fed, 11.7+/- 2.2 fmol taurine larva(-1) h(-1); unfed controls, 1.08+0.33 fmol tauri ne larva(-1) h(-1); means +/- S,E,M,), Fed larvae also synthesized tau rine from [S-35]methionine (18.4 fmol larva(-1) h(-1)), I, galbana con tained 5 fmol cell(-1) of cysteine and methionine (combined) and, base d on known feeding rates, we calculated that there were sufficient tau rine precursors in the algae to supply the taurine requirements of gro wing larvae, The lack of significant de novo taurine synthesis reporte d for adult bivalve molluscs has led to the conclusion that taurine is a dietary requirement, Our findings for larval forms differ in that t here is significant de novo synthesis of taurine during development.