FIG. 6.

Majority of Frx activity in the CSF is not from Cp. (A) Unlike serum and purified Cp, Frx activity in the <3-kDa fraction of CSF is not sensitive to sodium azide (2.5 mM). Data are means±SEM of 5 serum and 10 CSF samples analyzed in duplicate; ***p<0.001. (B) Unlike purified Cp that loses all Frx activity after heating, there is a minimal change in CSF samples. Data are means±SEM of five CSF samples analyzed in duplicate; ***p<0.001. (C) Unlike purified Cp, Frx activity in CSF is not reduced by repeated freeze–thawing. Data are means±SEM of five samples analyzed in duplicate. (D) The CSF Frx activity is resistant to Triton X-100. Data are means±SEM of four samples analyzed in duplicate. (E) Unlike purified APP, Frx activity in CSF is not sensitive to zinc (10 μM). Purified Cp is also unaffected by zinc. Data are means±SEM of five CSF samples; **p<0.01. (F) As opposed to H₂O₂, the <3-kDa fraction of CSF lacks copper oxidase activity. Each point represents mean±SEM of two samples analyzed in duplicate.