A series of single alanine substituted analogs of amyloid beta peptide (25-35) were tested for their ability to activate the phospholipases of cultured LA-N-2 cells. Substitution of alanine for the amino acids 29-34 prevented the activation of phospholipases A2 and D. In addition substitution of alanine at 28 prevented phospholipase D but not phospholipase A2 activation. All the alanine substitutions, except for positions 33 and 35, blunted phospholipase C activations. There were no activations by scrambled amyloid beta peptide. (C) 1997 Federation of European Biochemical Societies.