I performed activity assays on cell lysates following the protocol described in Osellame et al. 2013.
I purchased 4-Methylumbelliferyl β-D-glucopyranoside from Sigma (M3633) and in the datasheed it is described as soluble in N,N-dimethylformamide
(DMF, 50 mg/ml), but for enzyme assays, it suggests to dissolve it at
5 mM (1.7 mg/ml) in water or 0.2 M sodium citratephosphate
buffer. I tried the second option and I couldn't get a fully solubilized solution (some white particles were still present in suspension in the buffer) which affected the compound concentration.
Any idea about why I am getting this problem and how to solve it? I have to say that this problem occurs randomly and is not associated to a specific batch of 4-Methylumbelliferyl β-D-glucopyranoside or buffer I am using.
Thanks for any help.