Fig 2. The effect of NaCl on frozen α₂M preparations.

(A) Images of native PAGE (3–8% Tris-acetate) gels showing α₂M stored in 20 mM sodium phosphate buffer, pH 7.4, in the presence or absence of 150 mM NaCl (4°C or -20°C, 20 days). LN indicates that the sample was rapidly frozen in liquid nitrogen prior to storage at -20°C. Also shown is the position of α₂M* (generated by treatment with 400 mM NH₄Cl in PBS overnight). (B) Corresponding bisANS fluorescence measurements for α₂M as described in (A). The results shown are the mean bisANS fluorescence (n = 3±SD) in AFU. (C) Trypsin activity assay showing the rate of BAPNA conversion to p-nitroaniline by trypsin-α₂M complexes generated using α₂M as described in (A). The results shown are the mean BAPNA conversion rates (n = 3±SD). * Denotes significant increases in bisANS fluorescence of α₂M stored at -20°C compared to a matched sample stored at 4°C. ^v Denotes significant decreases in the rate of BAPNA conversion to p-nitroaniline by trypsin-α₂M complexes generated using α₂M stored at -20°C compared to a matched sample stored at 4°C (both Student’s t-test p < 0.01).