The Influence of Ethylene Glycol on the Enzymatic Adenosine Triphosphatase Activity and Molecular Conformation of Fibrous Muscle Proteins

Delayed dissociation of in vitro moving actin filaments from heavy meromyosin induced by low concentrations of Triton X-100

The in vitro motility of fluorescent actin filaments over heavy meromyosin (HMM) was studied in the presence of the nonionic detergent Triton X-100. Below 0.004% Triton X-100 concentration, motility was not affected. Above 0.007%, motility was not observed because actin filaments were dissociated from HMM. In the Triton X-100 concentration range of 0.004-0.007%, the sliding actin filaments dissociated from HMM with a delay. The dissociation delay time decreased with increasing Triton X-100 concentration, increasing ATP (adenosine-5'-triphosphate) concentration, and increasing temperature. The delayed acto-HMM dissociation was absent when weak-binding kinetic intermediates of the myosin ATPase cycle (M.ATP and M.ADP-Pi) were used. The presence of sliding movement was necessary to evoke the delayed acto-HMM dissociation. The acto-HMM dissociation delay was independent of actin filament length. For a given Triton X-100 concentration, the dissociation delay time was found to be inversely proportional to sliding velocity, indicating that actin filaments travel a more or less constant distance prior to dissociation from HMM. The actin-activated HMM ATPase activity was not inhibited by Triton X-100; rather, it was slightly enhanced. The results imply the presence of a motility-associated conformational change in acto-HMM.

Modification of crossbridge states by ethylene glycol in insect flight muscle

Substitution of ethylene glycol for part of the solvent water changes the mechanical properties, structure and nucleotide binding of glycerol-extracted flight muscle fibres from the waterbug Lethocerus. On addition of ethylene glycol the rigor tension falls, rapidly and reversibly. With increasing glycol concentration the effect saturates at a non-zero tension. The isotonic stiffness is unchanged on adding ethylene glycol. Adding MgAMPPNP (adenylylimidodiphosphate) to a muscle fibre in 50% ethylene glycol causes a further rapid tension fall; above 100 microM AMPPNP the tension reaches zero. The isotonic stiffness of restretched muscle is then close to that of a relaxed fibre. Removal of MgAMPPNP from the bathing medium has no immediate mechanical effect. After several hours the isotonic stiffness rises to some extent; on removal of the glycol both tension and stiffness rise to rigor values within one minute. 3H-Labelled AMPPNP binds to muscle fibres in 50% ethylene glycol in a similar amount to the number of myosin heads present. The binding is tighter than that in aqueous solution and the nucleotide is only released very slowly. Upon removal of the ethylene glycol nucleotide is rapidly released. X-ray diffraction of muscle in 50% ethylene glycol reveals a highly ordered structure, in which both the 14 nm and the 38 nm layer lines are sharply sampled and are of intermediate values between rigor and relaxation. The two inner equatorial peaks are also of intermediate values. On adding MgAMPPNP the pattern resembles that of relaxed muscle. Upon removal of the nucleotide the pattern does not revert towards rigor but on removal of glycol it does. These results are interpreted in terms of changes within the myosin heads and their array within the filament lattice.

Alteration of the specificity of restriction endonucleases in the presence of organic solvents

The specificity of XbaI, SalI, HhaI, PstI, BamHI and SstI is relaxed in the presence of an organic solvent, such as 20% glycerol or 8% dimethylsulfoxide (DMSO). This alteration, very pronounced in some cases, requires an excess of enzyme, varies from one kind of enzyme to another and is highly dependent on the pH, the ionic strength, the nature of the metallic cofactor and/or the presence of a second organic solvent. Preliminary data concerning XbaI and BamHI used under conditions where the relaxation of specificity is moderate, suggest that some of the new ("pseudo") sites correspond to shortened sequences derived from the normal recognition sequence cleaved under the standard conditions of the reaction.

Cardiac myosin adenosinetriphosphatase activity. Modifying factors and comparison with skeletal muscle myosin adenosinetriphosphatase activity

Cardiac myosin prepared by any one of a number of modifications of the basic Szent-Gyorgyi method and cardiac myosin prepared by the lithium chloride-ammonium sulfate technique differ in two important respects: 1) Szent-Gyorgyi-prepared myosin solutions are inhomogeneous by both chemical and immunologic criteria; 2) the ATPase activity of Szent-Gyorgyi-prepared myosin is low in comparison to lithium chloride-ammonium sulfate prepared cardiac myosin. Evidence is presented in this paper showing that the reduced ATPase activity of Szent-Gyorgyi-prepared cardiac myosin is the result of inhibition of the enzyme, possibly by a nucleotide contaminant, and a "diluting" effect of other nitrogen-containing contaminants of low specific activity.

Many earlier studies indicate that cardiac and skeletal muscle myosin prepared by the Szent-Gyorgyi method differed strikingly in their ATPase activities. Comparison of lithium chloride-ammonium sulfate prepared cardiac and skeletal muscle myosin shows that skeletal muscle myosin has a slightly but significantly higher ATPase activity than canine cardiac myosin. A methodologic error was not excluded as the cause of this discrepancy. In a number of other characteristics, canine cardiac and skeletal muscle myosin ATPase activity was virtually identical.