Hello,
I am working on bacterial alkaline phosphatase, does anyone know a universal buffer to measure the activity of this enzyme? Different articles suggested different buffers.
Yes, there are many assay buffers and all of them are probably 'universal', in the sense that they will work to some extent. As there can be complex interplay between buffer type, pH, metal ion concentration and type of substrate, there are naturally many different perfectly reasonable assays in the literature.
A simple buffer to get started for a colorimetric assay would be 50mM Tris pH 8.6, 0.5mM pNPP, 2mM MgCl2. You may find it convenient to make this up a 2x buffer, and add pNPP from a 10x stock. Glycine buffer is often used instead of Tris, but it generally gives lower enzyme activities
The pH optimum for bacterial enzyme is often around pH 9, and you could just about push Tris buffer to that level if you want to maximise the activity. If you simply want to be able to measure activity, you don't need to spend too much time on optimisation. Almost any moderately alkaline condition + MgCl2 will give you some activity.
Here is a protocol that I've used for years with appropriate references.
Normal buffers can be used in a range of +/- 1 pH-unit around the pKa-value. "Universal" buffers have a wider working range, they use multivalent acids with closely spaced pKa-values. Examples include the McIlvaine-buffer (DOI:10.1016/S0021-9258(18)86000-8, pH 2.2-8, phosphoric and citric acid), and the Britton/Robinson-buffer (DOI:10.1039/JR9310001456, pH 2.5-9.8, citric, phosphoric and boric acid). The latter changes its pH linearly with addition of base.
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