Degradation of Soluble Amyloid β-Peptides 1–40, 1–42, and the Dutch Variant 1–40Q by Insulin Degrading Enzyme from Alzheimer Disease and Control Brains
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- Pérez, A., Morelli, L., Cresto, J.C. et al. Neurochem Res (2000) 25: 247. doi:10.1023/A:1007527721160
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Insulin degrading enzyme (IDE) is a metalloprotease that has been involved in amyloid β peptide (Aβ) degradation in the brain. We analyzed the ability of human brain soluble fraction to degrade Aβ analogs 1–40, 1–42 and the Dutch variant 1–40Q at physiological concentrations (1 nM). The rate of synthetic 125I-Aβ degradation was similar among the Aβ analogs, as demonstrated by trichloroacetic acid precipitation and SDS-PAGE. A 110 kDa protein, corresponding to the molecular mass of IDE, was affinity labeled with either 125I-insulin, 125I-Aβ 1–40 or 125I-Aβ 1–42 and both Aβ degradation and cross-linking were specifically inhibited by an excess of each peptide. Sensitivity to inhibitors was consistent with the reported inhibitor profile of IDE. Taken together, these results suggested that the degradation of Aβ analogs was due to IDE or a closely related protease. The apparent Km, as determined using partially purified IDE from rat liver, were 2.2 ± 0.4, 2.0 ± 0.1 and 2.3 ± 0.3 μM for Aβ 1–40, Aβ 1–42 and Aβ 1–40Q, respectively. Comparison of IDE activity from seven AD brain cytosolic fractions and six age-matched controls revealed a significant decrease in Aβ degrading activity in the first group, supporting the hypothesis that a reduced IDE activity may contribute to Aβ accumulation in the brain.