Andrew G. Szent-Györgyi

Meromyosins, the subunits of myosin☆☆☆

Abstract 1. 1. The isolation of the two subunits of myosin, obtained after short digestion by trypsin, is described. Based upon their molecular weight, they were termed L- and H-meromyosins (“L” stands for light, “H” for heavy). 2. 2. The meromyosins were obtained in native form. The L-meromyosin was crystallized. H-Meromyosin has the total ATPase activity and the capacity of combination with actin of the intact myosin molecule. 3. 3. The properties of the meromyosin molecules are described. 4. 4. The L-meromyosin has a molecular weight of 96,000 and is 550 A. long and 16 A. wide. The H-meromyosin has a molecular weight of 232,-000 and is 435 A. long and 29 A. wide. 5. 5. One myosin molecule consists of four L-meromyosins and two H-meromyosin molecules. It is proposed that the L-meromyosins are linked in series to a chain and the H-meromyosins are attached to them. 6. 6. It is suggested that the L-meromyosin is the contractile part of the myosin molecule. The results are discussed in relation to the structure and contraction of the myosin and muscle.Abstract 1. 1. The isolation of the two subunits of myosin, obtained after short digestion by trypsin, is described. Based upon their molecular weight, they were termed L- and H-meromyosins (“L” stands for light, “H” for heavy). 2. 2. The meromyosins were obtained in native form. The L-meromyosin was crystallized. H-Meromyosin has the total ATPase activity and the capacity of combination with actin of the intact myosin molecule. 3. 3. The properties of the meromyosin molecules are described. 4. 4. The L-meromyosin has a molecular weight of 96,000 and is 550 A. long and 16 A. wide. The H-meromyosin has a molecular weight of 232,-000 and is 435 A. long and 29 A. wide. 5. 5. One myosin molecule consists of four L-meromyosins and two H-meromyosin molecules. It is proposed that the L-meromyosins are linked in series to a chain and the H-meromyosins are attached to them. 6. 6. It is suggested that the L-meromyosin is the contractile part of the myosin molecule. The results are discussed in relation to the structure and contraction of the myosin and muscle.

Keto-aldehydes and cell division.

Many problems are left open in this article. Its publication may be excused by the suffering cancer causes, which urges the researcher to publish as soon as he thinks he may have found a new trail, which also may be taken by others. What emerges clearly is that SH groups, with their specific reactivities, offer a hopeful target in the search for cancerostatic substances, among which the natural repressor of cell division may hold out the most promise. The glyoxal derivatives also have antiviral properties (7, 16) and may be in the center of a hitherto unknown system of equilibria which deserves a thorough study. The low molecular weight of the glyoxal derivative reported justifies the hope of an early clarification of its structure, as well as its synthesis (17).

On the mechanism of action of chlorpromazine.

Chlorpromazine is shown to be a powerful electron donor. Observations are described supporting the assumption that the therapeutic action of this drug is connected with this property.

The reversible depolymerization of actin by potassium iodide

Abstract 1. 1. G-actin obtained from acetone-dried muscle polymerizes in 0.1 M KI after incubation in 0.6 M KI. 2. 2. G-actin prepared by depolymerizing F-actin by 0.6 M KI does not polymerize in 0.1 M KI. 3. 3. G-actin obtained by depolymerizing F-actin by 0.6 M KI in the presence of small concentrations of added adenosine triphosphate (ATP), adenosine diphosphate (ADP) or inosine triphosphate (ITP) polymerizes readily in 0.1 M KI. Adenosine monophosphate (AMP), inorganic pyrophosphate, or inorganic phosphate have no such protective action. 4. 4. Adenosine triphosphate, ADP, and ITP are effective maximally in amounts up to 5 × 10 −5 mole. 5. 5. The findings of Straub and Feuer that during polymerization ATP is dephosphorylated to ADP is confirmed. 6. 6. Contrary to the findings of Straub and Feuer no synthesis of ATP was observed during depolymerization, not even in the presence of ADP when depolymerization was reversible.Abstract 1. 1. G-actin obtained from acetone-dried muscle polymerizes in 0.1 M KI after incubation in 0.6 M KI. 2. 2. G-actin prepared by depolymerizing F-actin by 0.6 M KI does not polymerize in 0.1 M KI. 3. 3. G-actin obtained by depolymerizing F-actin by 0.6 M KI in the presence of small concentrations of added adenosine triphosphate (ATP), adenosine diphosphate (ADP) or inosine triphosphate (ITP) polymerizes readily in 0.1 M KI. Adenosine monophosphate (AMP), inorganic pyrophosphate, or inorganic phosphate have no such protective action. 4. 4. Adenosine triphosphate, ADP, and ITP are effective maximally in amounts up to 5 × 10 −5 mole. 5. 5. The findings of Straub and Feuer that during polymerization ATP is dephosphorylated to ADP is confirmed. 6. 6. Contrary to the findings of Straub and Feuer no synthesis of ATP was observed during depolymerization, not even in the presence of ADP when depolymerization was reversible.

The structure of light-meromyosin: an electron microscopic study.

Abstract Light-meromyosin crystals show a principal periodicity of 420 ± 25 A along the main axis with an additional structure in the electron microscope. This periodicity agrees with the value of the fundamental fiber period found in muscle by X-ray crystallography by Bear and by Huxley .

Depolymerization of light meromyosin by urea

Abstract Light meromyosin depolymerizes by urea into units of 4600 weight under specific conditions which are described. These units, called protomyosins, appear to be uniform as far as their size and shape is concerned but are different in their amino acid composition. The possible role of the protomyosins in the structure of light meromyosin and in contractility is discussed.

On the nature of the cross-striation of body muscle.

Abstract After the removal of globular proteins, solvents used for extraction of myosin remove from glycerol-pretreated body muscle a considerable amount of protein other than myosin, the quantity of which is sufficient to account for the differences in refraction between the A and I bands.

Observations on the electron microscopic structure of insect muscle.

Abstract Four electron micrographs are reproduced. The longitudinal section of the wing muscle of the house-fly shows the absence of the series elastic component and of the A and I bands. The possible bearing on the genesis of these bands is discussed. Mitochondria of the wing muscle of the bumble-bee show a tubular inner structure, while the mitochondria of the leg muscle show laminar formations.

Comments on the structure of myosin.

Abstract 1. 1. The purpose of the present study was to determine which of the possible structures of myosin are, in the light of hydrodynamic theory, consistent with the following considerations: first, that myosin is composed of heavy- plus light-meromyosin molecules in the ratio of 1 to 2; and, second, that the sedimentation coefficient of myosin is about 10% less than that of the heavy-meromyosin. 2. 2. The conventional equation relating the frictional ratio of elongated ellipsoids of revolution to their axial ratio was rearranged into a form which shows the mean coefficient of friction of the elongated ellipsoid of revolution in terms of the major semiaxis and the minor semiaxis of the ellipsoid. 3. 3. Limiting coefficients of friction were calculated for various models made up of four light meromyosin molecules plus two heavy-meromyosin molecules on the assumption of no change in shape of the meromyosins. Of the various models considered, the only one investigated which satisfies the conditions stated above in 1 consists of the four light-meromyosin molecules and the two heavy-meromyosin molecules arranged in a straight line. 4. 4. Limiting coefficients of friction were also calculated for various models made up of two light- and one heavy-meromyosin molecules, on the assumption of no change in shape of the meromyosins. The only model considered which satisfies the sedimentation and diffusion data obtained in experiments carried out in the cold is one in which the two light- and the one heavy-meromyosin molecules are arranged in a straight line. This consideration and that stated in 3 lead to the conclusion that, if myosin at room temperature is a polymer of two particles of the type existing in the cold, the polymerization must be end-to-end.

Actomyosin and muscular contraction

Abstract It is shown that the contraction of muscle, superprecipitation of its suspensions, superprecipitation of actomysin and contraction of actomyosin, elicited by ATP, are related phenomena. Differences in behavior, as for instance anisodiametry of shrinking in muscle and isodiametry of shrinking in unoriented actomyosin gels, can be explained by the differences in structure. The same is true for the difference of muscle and loaded actomyosin threads, the latter of which, contrary to muscle, lengthen under influence of ATP.