Changes in water binding upon complex formation have been measured for several specific sequence DNA binding proteins. Large numbers of water molecules are displaced in the binding reaction: approx. 100 for the binding of the galactose operon repressor, approx. 50 for CAMP receptor protein (CAP), and approx. 30-40 for the specific binding of the restriction nuclease Eco RI. These changes in hydration correlate approximately with the size of the DNA recognition sequence. In addition, the binding of a second galactose operon repressor to the naturally occurring 2 operator DNA fragmetn shows an additional release of water due to protein- protein interactions. Changes in hydration accompanying the binding of analogs of the antibiotic netropsin to specific DNA sequences are being measured. A correlation between water release and binding strength to different sequence has now been observed. The complete set of date of water release and binding energy from many different sequences will allow a quantitative analysis of the importance of the hydration forces observed in condensed systems for the specific binding of peptides and proteins to DNA in dilute solution. The electric birefringence of Acanthamoeba myosin II filaments has revealed a large change in LMM-HMM junction flexibility with ATP binding to myosin heads. In addition to the well established crossbridge motions of myosin heads, a concomitant change in filament stiffness coupled to ATP binding and hydrolysis appears involved in the force generation cycle of myosin.
