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

Abstract

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, K_m and V_max of 2.6 μM and 996 nmol.min⁻¹.ml⁻¹, respectively and was relatively stable at the optimum conditions (t_½ = 3 h). β-Amyloid peptide fragments Aβ_17–28 was the better inhibitor for nNOS (K_i = 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 Aβ_17–21 [Leu₁₇ – Val₁₈ – Phe₁₉ – Phe₂₀ – Ala₂₁] and glycine zipper motifs within the peptide fragment Aβ_17–35 were critical in binding and in fibrillogenesis confirming that nNOS was amyloidogenic catalyst.

Keywords::

• Neural nitric oxide synthase
• Alzheimer disease; inhibition
• amyloid peptides

Acknowledgements

The financial assistance from The Medical Research Council (South Africa) toward this research is hereby acknowledged.

Declaration of interest

The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.