Scientists have learned that the amyloid-beta peptide is responsible for forming amyloid plaques. This peptide is part of a much larger protein called the amyloid precursor protein (APP), which is thought to be lodged in the cell membrane of dendrites, the short, branching extensions of neurons (fig. 5.7). Two separate enzymes cut through the precursor protein, each in a different place, releasing the amyloid-beta peptide (fig. 5.7). Once released from the cell membrane, the peptide floats in the space outside the neuron.
