EFFECT OF DIAZONIUM DERIVATIVES ON MYOSIN A ADENOSINE TRIPHOSPHATASE .2. A POSSIBLE CONFORMATIONAL CHANGE INDUCED BY ATP

Myosin was treated with p-nitroaniline diazonium fluoroborate (NDF) to modify its structure chemically.1. NDF at a molar ratio of 3.6: 1 to myosin subunit strongly inhibited the Ca++-ATPase [EC 3.6.1.3] activity, but slightly suppressed the EDTA-ATPase activity. Conversely, when 1 mM ATP or ADP was present in the coupling reaction mixture, the diazonium compound suppressed the activity of EDTA-ATPase but only slightly inhibited Ca++-ATPase. Two moles of ATP per mole of myosin subunit were enough to bring the above-mentioned change of the inhibition pattern of ATPase to completion. AMP had no effect.2. With 1 mM ITP or PP1 in the presence of Mg++, NDF inactivated both Ca++-and EDTA-ATPases.3. Inhibition of the ATPase activity by NDF decreased with increasing pH of the coupling reaction mixture.4. The catalytic properties of myosin modified with NDF in the presence and absence of ATP also differed in pH dependence, the K m values and Mg++-and K+-ATPase activities. The properties of the former were almost the same as those of myosin modified with diazobenzene-p-sulfonate which had been investigated by us.On the basis of the experimental data obtained, the conformational change induced by ATP and its analogues was discussed. © 1969 BY THE JOURNAL OF BIOCHEMISTRY.