Investigation of the active centre of myosin by the method of paramagnetic labels

The present paper is concerned with study of the active centre of myosin by the method of paramagnetic labels. We have studied the interaction of iminoxyl radicals on the basis of iodoacetamide (I) and parachloromercurybenzoate (II) with myosin of rabbit muscles. Both reagents activate the enzyme preferentially blocking the activating group of sub-fragment one (S1). The sulphydryl group of S1 is located on the side of the active centre and the activation of the enzyme on modification of this group is apparently of an allosteric type. According to the calculation made the distance between the sulphydryl group of S1 and the active centre is 15-17 rA. On interaction of the active centre with the substrates two local conformational transitions are observed of an allosteric character. In the temperature interval 33-48 °C a largescale conformational transition is observed affecting both the active centre and the activating group of S1. The method of the paramagnetic probe has established the presence of charges close to the S1 group. From the experimental results it may be assumed that the two "heads" (enzymatically active globular enzyme of the myosin molecule) are identical and that they perform different functions in native protein.