Association of β-amyloid peptide fragments with neuronal nitric oxide synthase: Implications in the etiology of Alzheimers disease.

Neuronal nitric oxide synthase (nNOS) was purified on DEAE-Sepharose anion-exchange in a 38% yield, with 3-fold recovery and specific activity of 5 µmol.min⁻¹.mg⁻¹. The enzyme was a heterogeneous dimer of molecular mass 225 kDa having a temperature and pH optima of 40°C and 6.5, Km and Vmax of 2.6 μM and 996 nmol.min⁻¹.ml⁻¹, respectively and was relatively stable at the optimum conditions ( t½ == 3 h). β-Amyloid peptide fragments Aβ17-28 was the better inhibitor for nNOS (Ki == 0.81 µM). After extended incubation of nNOS (96 h) with each of the peptide fragments, Congo Red, turbidity and thioflavin-T assays detected the presence of soluble and insoluble fibrils that had formed at a rate of 5 nM.min⁻¹. A hydrophobic fragment Aβ17-21 [Leu17 - Val18 - Phe19 - Phe20 - Ala21] and glycine zipper motifs within the peptide fragment Aβ17-35 were critical in binding and in fibrillogenesis confirming that nNOS was amyloidogenic catalyst. [ABSTRACT FROM AUTHOR]

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