The reaction of a positively-charged N-ethylmaleimide derivative with actin and myosin subfragment-1

• 1.1. A positively-charged N-ethylmaleimide (NEM) derivative, 4-(N-maleimido)benzyltrimethylammonium iodide (MBTA), bound to Cys-373 of G-actin.
• 2.2. The reaction of MBTA with G-actin was much faster than that of NEM or of 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB).
• 3.3. MBTA-labeling to myosin subfragment-1 (S-l) has qualitatively the same effects on S-1 ATPase activity as NEM-labeling.
• 4.4. The reaction of MBTA with S-1 was slower and less specific than that of NEM.