Amyloid proteins extracted from the amyloid cores of neuritic plaques are considerably racemized at their Asp residues. To assess the impact Of D-Asp on amyloid beta(1-42) conformation and on initiation of amyloid fibril formation, we used wild-type amyloid beta(1-42) and analogs in which D-Asp was substituted for L-Asp at residues 1, 7, 23, and all combinations of these residues. Amyloid fibril formation was enhanced by D-ASP(23); modulation of Asp chirality at N-terminal position 1 blocked this enhancement and modulation at position 7 augmented it. Knowledge of such chirality modifications may help to develop potent inhibitors of amyloid fibril formation. (C) 2007 Elsevier Inc. All rights reserved.