LAUSR

&NA; Compelling evidence suggests a crucial role of amyloid beta peptides (A&bgr;(1‐40/42)) in the etiology of Alzheimer's disease (AD). The N‐terminal truncation of A&bgr;(1‐40/42) and their modification, e.g. by glutaminyl cyclase (QC), is expected to enhance the amyloid toxicity. In this work, the MALDI‐TOF mass spectrometry application proved N‐terminal cleavage of A&bgr;(1‐40/42) by purified dipeptidyl peptidase IV (DPPIV) in vitro observed earlier. The subsequent transformation of resulted A&bgr;(3‐40/42) to pE‐A&bgr;(3‐40/42) in QC catalyzed glutamate cyclization was manifested. Hence, consecutive conversion of A&bgr;(1‐40/42) by DPPIV and QC can be assumed as a potential mechanism of formation of non‐degrading pyroglutamated pE‐A&bgr;(3‐40/42), which might accumulate and contribute to AD progression. The in vitro acceleration of A&bgr;(1‐40) aggregation in the simultaneous presence of DPPIV and QC was shown also.