APP can also be processed by a-secretase, which cleaves within the Ab domain between Lys⁶⁸⁷ and Leu⁶⁸⁸ and produces a large soluble a-APP domain and the C-terminal fragment containing P3 and C83. The latter can then be cleaved by g-secretase at residue 711 or 713 to release P3 fragment. This pathway does not yield Ab peptide. Hence, shunting APP towards the a-secretase pathway may have a beneficial effect in lowering Ab peptide levels. It is reported that a-secretase shares many of its properties with the secretase that cleaves angiotensin-converting enzyme and is believed to be a zinc metalloproteinase of the ADAMs family (variously ADAM9, ADAM10 and ADAM17/TACE have been implicated). Muscarinic agonists (M1 and M3) and some PKC activators are reported to enhance a-secretase activity and are under consideration for their therapeutic value as AD treatment tools.