Myosin and adenosinetriphosphatase

The calcium-signalling saga: tap water and protein crystals

Of the approximately 1,400 grams of calcium that are in the human body, less than 10 grams manage to escape being trapped in the skeleton and teeth. These few grams might be an insignificant quantity, but they are extraordinarily significant qualitatively. They circulate in the blood and extracellular spaces, and penetrate cells to regulate their most important activities.

Recurring views on the structure and function of the cytoskeleton: a 300-year epic

Some unnoticed or seldom remembered precedents of current views on biological motion and its structural bases are briefly outlined, followed by a concise recapitulation of how the present theory has been constructed in the last few decades. It is shown that the evolution of the concept of fibers as main constituents of living matter led to hypothesizing microscopic structures closely resembling microtubules in the 18th century. At the beginning of this period, fibers sliding over each other and driven by interposed moving elements were envisioned as the cause of muscle contraction. In the following century, an account of the mechanism of myofibril contraction visualized longitudinal displacements of myosin-containing submicroscopic rodlets. The existence of fibrils in the protoplasm of non-muscle cells, a subject of long debate in the second half of the 19th century, was virtually discarded as irrelevant or fallacious 100 years ago. The issue resurfaced in the early 1930s as a theoretical notion--the cytosquelette--nearly two decades before intracellular filamentous structures were first observed with electron microscopy. The role originally assumed for such fibrils as signal conductors is nowadays being reappraised, although under new interpretations with a much wider significance including modulation of gene expression, morphogenesis, and even consciousness. Since all of the above ancestral conceptions were eventually abandoned, the corresponding current views are, to a certain extent, recurrent.

The proteins associated with contraction in lamellibranch ‘catch’ muscle

Pecten ‘actomyosin’ as prepared by the usual dilution-precipitation procedure is reasonably pure only when obtained from the striated adductor; when prepared from the smooth tonic adductor it consists of a protein mixture of about 1/3 actomyosin ( AM ) and ⅔ tropomyosin A ( TM A ; paramyosin). This admixture accounts for the previously reported differences in adenosine triphosphatase ( ATP -ase) activity of crude ‘ AM ’ from the two types of adductor muscles, since, after purification, all the biological activity characteristic of contractile proteins ( ATP -ase activity, ATP -sensitivity and ‘contractility’) is associated with AM alone. In presence of ATP this latter can also be dissociated into actin and myosin. After purification by salting out, the myosin is quite distinct from TM A in its solubility properties and sedimentation constant, and, unlike tropomyosin but like rabbit myosin, it possesses ATP -ase activity and combines with rabbit actin to form a synthetic or ‘hybrid’ actomyosin with an ATP -sensitivity of 45%. The presence in adductor muscles of a conventional actomyosin and myosin in addition to TM A makes it unlikely that the latter protein replaces the classical contractile proteins functionally in ‘catch’ muscle.

Characterization of myosin heavy chain by cyanogen bromide peptide maps

Procedures have been developed for the preparation of pure myosin heavy chain (h-myosin) by preparative gel electrophoresis, and for the characterization of h-myosin by cyanogen bromide peptide mapping. Major sources of error are the oxidation of methionine and the proteolytic splitting of the chain during purification. These errors have been eliminated. A peculiar feature is the doubling or quadrupling of a peptide of molecular weight 17 000. The results show structural differences between isomyosins derived from myonal types within the same animal, as well as interspecies differences.

Enzymatic activities and ATP-induced fluorescence enhancement of myosin from fast and slow skeletal and cardiac muscles

The maximal ATP-induced enhancement of fluorescence and the dependence of this enhancement on ATP concentration were determined for myosins from fast and slow skeletal and cardiac muscle of the rabbit. With myosins from slow and cardiac muscle modifications in the preparative procedure and chromatography on DEAE-Sephadex were required to obtain preprations which were free of actin, which exhibited the maximal fluorescence enhancement and which bound two moles of ATP per mole of myosin. Since the fluorescence enhancement of cardiac and slow muscle myosins is labile at slightly alkaline pH, it was also necessary to minimize incubation at pH greater than 7 in order to attain the maximal enhancement. With fast muscle myosin the changes in preparative procedure, together with chromatography, led to a 50 to 100% increase in the steady-state rate of ATP hydrolysis and fluorescence enhancement, without changing the maximal binding of ATP. From a comparison of the rate of steady-state hydrolysis of ATP with the rate of decay of the enhanced fluorescence, it appears that for all three myosins, both ATP binding sites have the same enzymatic activity, the steady-state rate per site being slower for cardiac and slow muscle myosins than for fast muscle myosin.

Comparative studies on myosin ATPase of a flying and nonflying bird

Myosin was purified from the flight muscles of a flying (pigeon) and a nonflying (fowl) bird. Ki (ADP) of myosin ATPase of pigeon is higher, but the Km (ATP) is lower than that of fowl. The specific activity (mumole of Pi liberated/min/mg protein) is higher for the fowl. A0.5 (CaCl2) of myosin of both pigeon and fowl is similar. However, the two proteins differ in their interactions with ADP, ATP and p-chloromercuribenzoate. The two proteins have the same tyrosine, tryptophan and sulfhydryl contents. The electrophoretic patterns of the two myosins on SDS-polyacrylamide gels are different. These studies show significant molecular differences in the myosin derived from the flight muscles of a flying (pigeon) and a nonflying (fowl) bird.

The relation between myosin adenosinetriphosphatase activity and inactivation of myosin under alkaline conditions of heart muscles in mammals of different size

ATPase activity of myosin in the heart muscle of the mouse, rat, guinea-pig, rabbit and pig was studied at neutral pH and under mild alkaline conditions. At neutral pH the ATPase activity of myosin is inversely related to body size of the animal species. The decrease of ATPase activity of myosin after alkaline preincubation depends on the degree of ATPase activity of intact myosin, i.e. myosin from the heart of the mouse exhibits high ATPase activity ae same relationship was found, when comparing myosin of new-born and adult heart muscle. It is concluded that the rate of alkaline inactivation of heart myosin is directly related to the degree of ATPase activity of intact myosin in all animals.

Intracellular calcium movements in skinned muscle fibres

1. Force development and (45)Ca movement between the internal membranes and the myofilament space were measured in segments of skinned muscle fibres.2. At 20 degrees C calcium ions in the myofilament space of calcium loaded fibres caused the internal membranes to release a substantial amount of calcium which produced a large force spike. Calcium produced a similar force spike in fibres containing only the physiological level of calcium when the temperature was lowered to about 6 degrees C.3. The force spike at 6 degrees C was inhibited when the magnesium concentration in the bathing solution was increased from 1 to 6 mM. The pattern of force development in preparations transferred directly from oil to a free calcium solution indicated that the normal concentration of Mg(2+) in the myofilament space of intact fibres is of the order of 10(-3)M.4. A possible role for the regenerative calcium release mechanism in the physiological activation of muscle fibres is suggested.

Biological activity and the 3-methylhistidine content of actin and myosin

1. The 3-methylhistidine content of myosin varies according to muscle type. It is highest in myosin from white skeletal muscle and lower values are obtained from myosin of red skeletal and smooth muscle. 2. The 3-methylhistidine content of actin was similar in all of the types of muscle from which it was isolated. 3. The 3-methylhistidine of rabbit actin is localized in a single tryptic peptide that was readily modified during fractionation procedures. 4. Photo-oxidation studies indicated that the 3-methylhistidine residues are not essential for adeonsine triphosphatase and actin-combining activities of myosin. 5. During photooxidation G-actin lost completely the ability to polymerize to the F form before all the 3-methylhistidine was destroyed.

Regulation of cardiac muscle contractility

The heart's physiological performance, unlike that of skeletal muscle, is regulated primarily by variations in the contractile force developed by the individual myocardial fibers. In an attempt to identify the basis for the characteristic properties of myocardial contraction, the individual cardiac contractile proteins and their behavior in contractile models in vitro have been examined. The low shortening velocity of heart muscle appears to reflect the weak ATPase activity of cardiac myosin, but this enzymatic activity probably does not determine active state intensity. Quantification of the effects of Ca(++) upon cardiac actomyosin supports the view that myocardial contractility can be modified by changes in the amount of calcium released during excitation-contraction coupling. Exchange of intracellular K(+) with Na(+) derived from the extracellular space also could enhance myocardial contractility directly, as highly purified cardiac actomyosin is stimulated when K(+) is replaced by an equimolar amount of Na(+). On the other hand, cardiac glycosides and catecholamines, agents which greatly increase the contractility of the intact heart, were found to be without significant actions upon highly purified reconstituted cardiac actomyosin.

Adenosinetriphosphatase activity of cardiac myosin. Comparison of the enzymatic activities and activation by actin of dog cardiac, rabbit cardiac, rabbit white skeletal and rabbit red skeletal muscle myosins

Examination of the ATPase activities of rabbit cardiac, rabbit red skeletal and rabbit white skeletal muscle myosins has demonstrated the existence of two types of myosin. One type, characterized by the higher ATPase activity, is present in white skeletal muscle; the other is found in red skeletal and cardiac muscle. The differences between myosin preparations could not be attributed to varying degrees of actin contamination nor to changes occurring in the myosins during the preparative procedure. Chromatography of dog cardiac myosin on DEAE-cellulose showed a single component. No differences were observed between the cardiac myosins of the dog and rabbit.

Activation of the ATPase activity of cardiac myosin by Ca ++ was less than that of white skeletal myosin while the extent of inhibition by Mg ++ was similar for both. The stoichiometry of the interaction with actin of both cardiac and white skeletal myosins was similar but actin caused less activation of the cardiac myosin ATPase. Cardiac and white skeletal actins showed no differences in their abilities to activate myosin ATPase activity, which is in accord with previously documented similarities in the structures of these actins.

Comparison of the present findings with previously reported mechanical measurements made with intact muscles does not indicate that the intrinsic level of myosin ATPase activity determines the maximal tension developed during the active state. On the other hand, there may be a direct relationship between shortening velocity and myosin ATPase activity.

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.

An electron microscope study of canine cardiac myosin and some of its aggregates

The morphology of the canine cardiac myosin molecule has been investigated in the electron microscope with Hall's mica-replica technique. The molecule is an elongated rod (shaft) of nonuniform diameter with a globular expansion (head) on one end. Statistical analysis of the lengths of 1908 molecules showed that the mean length was 1610 +/- 250 A; the mean length of the head was 210 +/- 20 A; and the diameter of the head and that of the shaft were 35 to 40 and 15 to 20 A, respectively. About one-third of the molecules had single or multiple, fairly sharp, angulations along their shafts. Rarely, some details of the substructure of the molecule have been observed. Large, spindle-shaped aggregates, measuring 0.5 to 1 micro in length and 50 to 100 A in diameter, were produced by dilution of the myosin solutions. These aggregates were readily visualized in the electron microscope by means of Huxley's negative-staining technique. Projections often were visible along the length of the aggregates except at a central zone where they were frequently absent. The aggregates resembled the thick myofilaments of the myocardium and appeared similar to those produced by Huxley from skeletal myosin solutions.

THE PREPARATION OF ADENOSINE 5'-PYROPHOSPHATE BY A NON-ENZYMIC METHOD

1. A non-enzymic method for the preparation of adenosine 5'-diphosphate is described, in which the terminal phosphate of adenosine 5'-triphosphate is transferred to methanol in the presence of hydrochloric acid. The final purified product can be obtained in 60% yield. 2. Experiments with [(14)C]methanol showed that no methylation of the adenosine diphosphate occurs during the reaction. 3. Confirmation that the pyrophosphate moiety of the adenosine diphosphate produced was in the 5'-position was obtained by: (a) periodate oxidation; (b) treatment with apyrase and examination of the resulting adenylic acid isomer by paper chromatography. 4. The method appears to be generally applicable to the preparation of nucleoside 5'-diphosphates from the corresponding nucleoside 5'-triphosphates.

INFLUENCE OF SUBSTRATE-COFACTOR RATIOS ON PARTIALLY PURIFIED INORGANIC PYROPHOSPHATASE ACTIVITY AT ELEVATED TEMPERATURES

Mathemeier, Paul F. (Oregon State University, Corvallis), and Richard Y. Morita . Influence of substrate-cofactor ratios on partially purified inorganic pyrophosphatase activity at elevated temperatures. J. Bacteriol. 88: 1661–1666. 1964.—Inorganic pyrophosphatase of Bacillus stearothermophilus was studied for optimal substrate-cofactor ratios at 60 to 100 C. Mg ++ was the primary cofactor, and Co ++ resulted in 50% enzyme activity at 60 C. The pH optima differed for the Mg ++ activated and Co ++ activated pyrophosphatase. At 80 C and above, Co ++ replaced Mg ++ as the optimal cofactor in the enzyme reaction. The optimal ratio of pyrophosphate to Mg ++ varied from 2 to 0.25, dependent on enzyme concentration. The optimal pyrophosphate-cobalt ratio was constant at 1.0. The enzyme catalyzed appreciable pyrophosphate hydrolysis at 95 C.

Comparison of Tropomyosins from Cardiac and Skeletal Muscle

No differences were found between the sedimentation coefficients, intrinsic viscosities, amino acid contents, and peptide patterns resulting from tryptic digestion of rabbit cardiac and skeletal tropomyosins. From sedimentation and viscosity data, the molecular weights of cardiac and skeletal tropomyosins were estimated to be 54,800 for both. This value is similar to previous estimates of the molecular weight of rabbit skeletal tropomyosin.

No evidence was obtained for the existence in heart muscle of tropomyosin A . Of the three more abundant contractile proteins of the heart, myosin, actin, and tropomyosin, only myosin appears to differ from its skeletal counterpart.