Figure 7. γ-Secretase is not affected by Aβ peptides present in free solution.

(A) The lanes labeled as “free reaction” represent Aβ products after 4 hours of routine γ-secretase reaction at half saturating C99 substrate ([C99] = 0.45 µM). The lanes labeled as “+10 nM Aβ 1–42” and “+10 nM Aβ 1–40” represent “free reaction” premixed with synthetic Aβ 1–42 or Aβ 1–40 in a concentration equivalent that corresponds to 4 hours of free reaction. The lanes labeled “+21F12” and “+2G6” represent “free reaction” that was premixed with antibodies specific for Aβ42 or Aβ40 respectively. Both 2G6 and 21F12 antibodies bind the matching Aβ peptides very efficiently as indicated by a complete removal of the corresponding Aβ bands in the reactions with protein G beads (samples labeled as “21F12 and prot. G” and “2G6 and prot. G”). The lane “Aβ std 1-x” represents synthetic peptides as mobility standards. (B) AICD production was measured at half-saturating C99 substrate (0.45 µM) in assays that were premixed with increasing concentrations of synthetic Aβ 1–38, Aβ 1–40, Aβ 1–42, or Aβ 1–44.