Retinoid metabolism (LRAT, REH) in the yolk-sac membrane of Japanese quail eggs and effects of mono-ortho-PCBs

摘要

Retinoids stored in the avian egg are essential for normal development, however, laboratory and field experiments suggest that they are affected by environmental contaminants. Lecithin:retinol acyltransferase (LRAT) activity was detected in the microsomal fraction of the yolk-sac membrane of the Japanese quail at day 6 of development. LRAT activity was maximal at pH 7.0 having apparent kinetic parameters of K_m=1.35 muM and V_(max)=0.21 nmol/mg protein/h and was inhibited by the sulfhydryl modifying agent N-ethyl-maleimide. Retinol ester hydrolase (REH) activity in the microsomal fraction of the yolk-sac membrane was stimulated by the bile salt analogues 3-[(3-cholamidopropyl) dimethyl-ammonio]-1-propane sulfonate and was maximal at pH9.0 with apparent K_(m)=77 muM and V_(max)=34.3 nmol/mg protein/h. Injection of the PCB congener 2,3,3',4,4'-pentachlorobiphenyl increased both REH and LRAT activities, whereas 2,3,3',4-tetrachlorobiphenyl stimulated LRAT. Yolk retinol concentration and the molar ratio retinol:retinyl palmitate were lower in the exposed eggs. Yolk retinol concentration decreased as LRAT increased (R~2=0.89) suggesting that certain PCB congeners may affect vitamin A mobilization in ovo by increasing LRAT activity in the yolk-sac membrane.