sentence: The flagella were extracted with 0.2 % Nonidet P-40 in HMDEK solution ( 30 mM Hepes , 5 mM MgSO , 1 mM dithiothreitol , 1 mM EGTA , and 50 mM potassium acetate , pH 7.4 ) and centrifuged to remove the membrane and matrix fraction , then the resultant axonemes were suspended in HMDEK ( Witman , 1986 ) .