D.R. Kominz

The amino acid composition of actin, myosin, tropomyosin and the meromyosins

Abstract The amino-acid composition of actin, tropomyosin, myosin, L-meromyosin, and H-meromyosin has been determined by the Moore and Stein Chromatographic technique. The data obtained on the meromyosins when added up yield the amino acid composition of myosin. Tropomyosin and actin taken in equal proportion also approximate myosin, although the agreement with some of the amino acids is poor. Although not permitting the conclusion that myosin is a compound of actin and tropomyosin, the data strongly suggest a relationship, and do not rule out the possibility that actin and tropomyosin may be subunits in the myosin molecule.

A subunit of myosin

Abstract 1. 1. Treatment with 0.1 M Na 2 CO 3 releases from myosin a protein of about 29,000 molecular weight, which seems to be closely related to the material released from myosin by concentrated urea. 2. 2. The amino acid composition is presented. A relatively large amount of phenylalanine is present, in agreement with prediction for the subunit of myosin postulated by Laki. 3. 3. The C-terminal residue is isoleucine. The two C-terminal isoleucines of myosin are probably due to the presence of two of these subunits. 4. 4. This subunit is distinct from the tropomyosin-like subunit of myosin.

The amino acid composition of bovine prothrombin

Abstract The full amino acid composition of bovine prothrombin has been measured by using ion-exchange chromatography. In addition, other methods were used for the estimation of tyrosine, tryptophan, phenylalanine, and amide ammonia. Cysteine-cystine were estimated as cysteic acid. Eighteen amino acids and hexosamine are represented, glutamic acid, aspartic acid, and arginine being present in highest weight percentage. There is no resemblance between the known amino acid composition of serum albumin and that of prothrombin, though the two proteins are closely related with regard to their physicochemical characteristics in many respects.

Tropomyosin, myosin and actin from the blowfly, Phormia regina

Abstract 1. 1. Purified tropomyosin has been prepared from adult and larval stages of the blowfly, Phormia regina ; purified myosin and actin have been prepared from the adult stage only. Special procedures were required in the preparation of all three proteins. 2. 2. The amino acid compositions of these four purified proteins have been determined and compared to those of the corresponding rabbit proteins. The charged residues of Phormia tropomyosins are the same as those of lobster and most molluscs. Although there is no significant difference in amino acid composition between the two insect tropomyosins, fingerprint patterns of their tryptic digests suggest that structural differences may exist. 3. 3. The sedimentation rate, molecular weight, and intrinsic viscosity of adult Phormia tropomyosin are less than those of the more polymerizable larval protein. The adult values are: S 20 0 = 2.53, M 0 = 65 600, [ η ] = 0.23. The sedimentation rate and intrinsic viscosity of rabbit skeletal tropomyosin have been found to be comparable to those of the Phormia tropomyosins. 4. 4. Optical-rotary-dispersion studies show 100% ∞-helical configuration of the two insect tropomyosins, and the hydrodynamic measurements favor a 2-stranded structure.

Interactions of calcium and native tropomyosin with myosin and heavy meromyosin

Abstract It is confirmed that the presence of native tropomyosin is required in order for the removal of Ca ++ to cause inhibition of the Mg ++ -activated ATPase of actomyosin and acto-heavy-meromyosin. Native tropomyosin is present in routinely purified samples of myosin at levels of 0.7–2.3%; such quantities inhibit the actomyosin ATPase by 30–60% upon removal of Ca ++ . Titration with mercurial at low ionic strength causes a loss of actomyosin ATPase; it causes an even greater loss of the inhibition upon removal of Ca ++ . If the mercurial is added in the presence of ATP, greater loss of the ATPase occurs than if the mercurial is added in the absence of ATP. It is proposed that binding of ATP at a second site (distinct from the substrate-binding site) either potentiates or blocks the inhibitory conformational change caused by mercurial binding, depending on the ionic strength.

Molecular changes in myosin caused by methylmercuric hydrome

Abstract An ultracentrifugal study has been made on myosin treated with methylmercuric hydroxide. 1. 1. Myosin is transformed by tritration of its -SH groups with methylmerucuric hydroxide to a faster-sedimenting product. This occurs in the same range of methyl-mercuric hydroxide titration at which the calcium-activated ATPase activity is inhibited. A parallelism can be demonstrated between the loss of ATPhase activity and the loss of myosin due to the transformation process. 2. 2. Complete titration of the -SH groups of myosin with methylmercuric hydroxide causes the release of a small subunit with sedimentation rate of 1.6 S, at 25° but not at 15°. 3. 3. These results suggest that the -SH groups whose titration causes inactivation of ATPase activity are responsible for the configurational integrity of the active site, and that release of the small subunit is not related to titration of these -SH groups.

The 3 S fragments of rabbit and crayfish myosin obtained by copper cyanide treatment.

Abstract Treatment with heavy-metal cyanides at alkaline pH splits both rabbit and crayfish myosins into three portions. The fraction salting out at 38–42% ammonium sulfate saturation has a sedimentation rate of about 3 S . The amino acid compositions of the 3 S fragments of rabbit and crayfish myosins are identical in respect to free acid, lysine, and arginine; they differ appreciably from paramyosin and tropomyosin in respect to these residues.

Role of swelling in muscle contraction

Abstract The two types of volume change occurring in muscle and in contractile protein systems have been defined. Theoretical examination has been made of the influence of hydrophobic group interactions upon these two volume changes. Three different contractile mechanisms have been proposed in which osmotic changes can occur. The most plausible mechanism for striated muscle does not require a cell membrane and can effect a load-sensitive division of energy between direct pull and lateral swelling.

The influence of native tropomyosin on the ATP threshold for turbidity development of actomyosin and myofibril suspensions

Abstract By using an ATP regenerating system to maintain constant ATP concentration, a marked drop in the ATP threshold for turbidity development is observed in the presence of EGTA 2 . This effect is abolished when native tropomyosin is destroyed by trypsin digestion or removed by mild alkaline washing of actomyosin. When fresh native tropomyosin is added to such modified actomyosin, it is incapable of restoring more than a small part of the turbidity threshold shift, although it restores the ATPase inhibition almost completely.