Fig. 6. Pulse chase of nicastrin in wild-type and PS-deficient cells. (A) Wild-type (WT) and PS1^–/–PS2^–/– (KO) MEFs were metabolically labeled for 15 minutes and chased for the indicated time periods. Nicastrin was immunoprecipitated as described. In WT MEFs, the amount of immature nicastrin decreases in time, while mature nicastrin slowly increases. Note that mature nicastrin is extremely stable. In PS1^–/–PS2^–/– MEFs, no mature nicastrin is observed. Immature nicastrin degrades slowly. (B) WT and PS1^–/–PS2^–/–MEFs were metabolically labeled for 15 minutes and chased for the indicated time periods. APP was immunoprecipitated as described. Note the rapid degradation of both mature (APP_m) and immature APP (APP_i). (C) Graph showing immature/mature nicastrin as a function of time.