A, Western blot analysis of APP holoprotein (top) and APP C-terminal fragments (bottom) in 1% CHAPS brain extracts. Twenty micrograms of total protein from ∼2 month-old progeny of BACE1 transgenics crossed to Tg2576 (APP cDNA) transgenic animals were run on 4-12% Bis-Tris gradient gels, transferred to polyvinylidene difluoride membrane, and blotted with APP C-terminal polyclonal antibody 369. On the left are sizes of molecular mass makers in kilodaltons. B, quantitation of relative band intensities of APP C-terminal fragments using chemiluminescence with each brain extract analyzed in triplicate. The ratio of CTF-β: (CTF-β+CTF-α) was compared in animals transgenic for both BACE1 and Tg2576 (n = 6) to animals transgenic for Tg2576 alone (n = 7). Double transgenics had significantly higher APP CTF ratios by two-tailed Student’s t test, p value = 0.0003. C, brain extracts from ∼2-month-old animals were analyzed by ELISA. BACE1/Tg2576 animals (n = 5) had significantly higher levels of Aβ1-40 compared with Tg2576 alone (n = 5) by two-tailed Student’s t test, p value = 0.0040.