I understand that the CMC of dodecyl maltoside is approx. 0.17 mM and for effective protein extraction, the detergent concentration is to be higher than that of CMC.
1) I would like to know how many folds higher? At what point does protein denaturation happens approximately i.e whether at 2 -fold or 3-fold of CMC
2) Could a stock solution be prepared of DDM and stored for further use? I am using the detergent for the first time and would like to know whether it would be stable when prepared and stored for long time. (Storage conditions, if any please)
Okay, starting from your 2nd question : it's better to prepare fresh detergent before your solubilisations, since DDM is a maltoside , the solution can be easily contaminated. Otherwise you can try and store it in -20°C but better starting each time.
1st question : That is more complicated, first of all, during extraction you need to be in a large excess of detergent (more then there are lipids) in order to destabilize membranes. 1% is a good starting concentration of DDM for solubilisation (at a protein concentration or 1-2 mg/mL), you can try with 2% or 0,5% you cannot solubilize with just 1-2 CMC (CMC = 0,0017%, it would be insufficient).
Secondly, mild detergents like DDM generally do not denaturate your protein, but you can screen for detergents that do the job. The problem is that the protein is delipidated, and that can influence on its activity and/or its structure. If you are planning to purify your protein, after solubilisation, you can lower the detergent concentration (adding 3-5 CMC (need for optimization) to your chromatography buffer. And if you purify your protein, do not concentrate it too much, because you will tend to form hydrophobic interactions and that will cause some aggregation. Yet again, the choice of detergent and its final concentration (in buffer or after dialysis) depends on your protein and the downstream applications that you plan to carry on.
my 5 cents:
10 - 20 % stock in DDW can be stored for weeks at 4C.
1% in solubilization and 0.05% for wash and elution buffers worked well for me.
Make DDM fresh if possible or store a 20% solution at -20.
1, 1.5 or 2% can be the initial trial concentration for solubilization. Add slowly from 20% stock.
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