Myosin Isozymes Research Articles

Type IIB to IIA fiber transformation in intermittently stimulated rabbit muscles

Long-term intermittent stimulation (10 Hz, 8 h/day, 7 wk) of the fast-twitch tibialis anterior results in a complete transformation of type IIB fibers to type IIA fibers. This is shown by the histochemical ATPase reaction and by a decrease in Ca2+-uptake ability by the sarcoplasmic reticulum. Furthermore, as shown by studies on bulk myosin and on single fibers, the LC1-to-LC3 light chain ratio is increased on sodium dodecylsulfate gel electrophoretograms, and there are changes in the myosin isozyme pattern manifested on pyrophosphate gels under nondissociating conditions. Thus the staining intensity of the slower moving putative LC1 homodimer band increases, and there is a difference in migration velocity between stimulated and unstimulated isozymes suggesting a possible difference in the heavy chain. This study underlines the importance of the stimulation schedule in determining whether a fast-to-slow transformation or a shift in subtype takes place.

Effects of denervation on the distribution of myosin isozymes in skeletal muscle fibers

The pattern of distribution of myosin isozymes was examined with respect to the fiber population in the denervated rat diaphragm. Myosin was demonstrated by indirect immunofluorescence using antibodies against chicken myosin and by localization of ATPase activity. In the normal diaphragm, a heterogeneous fast-twitch muscle, the component fibers react with antibodies against fast or slow myosin, but usually not with both. By 8 weeks after removal of the nerve supply, all fibers reacted with antibodies specific for fast myosin, and many reacted with anti-slow myosin as well. This indicates either that multiple forms of myosin coexist within individual muscle fibers or that a unique myosin(s) is present which has determinants in common with both fast and slow isozymes. This pattern was observed for at least 24 weeks after denervation. At all stages, the localization of alkali-stable and acid-stable ATPase activity correlated well with the response to anti-fast and anti-slow myosin, respectively. We conclude that the normal adult neuromuscular relationship is required for the preferential distribution of fast and slow myosins into different populations of fibers. New myosin is nevertheless synthesized in the absence of the nervous system, and characteristics of both fast and slow isozymes are evident even after prolonged denervation.

Changes in myosin isozymes during development of chicken gizzard muscle.

The distribution of myosin isozymes in embryonic and adult chicken gizzard muscle were examined by electrophoresis in a non-denaturing gel system (pyrophosphate acrylamide gel electrophoresis), and both light and heavy chains of embryonic and adult myosin isozymes were compared. In pyrophosphate acrylamide gel electrophoresis, there were three isozyme components in embryonic gizzard myosin, but only one isozyme in adult gizzard myosin. The mobility of the fastest migrating embryonic isozyme was similar to that of the adult isozyme. The three embryonic isozymes differ from each other in the light chain distribution. Two of them contain an embryo-specific myosin light chain, which is characterized by its molecular weight and isoelectric point, whereas the other embryonic myosin isozyme contained the same light chains as the adult myosin. The pattern of peptide fragments of embryonic heavy chain produced by digestion with alpha-chymotrypsin in the presence of SDS was not distinguishable from that of adult myosin heavy chain. Thus there are myosin isozymes specific to embryonic gizzard muscle which exhibit embryo-specific light chain compositions, but are similar to adult gizzard myosin in their heavy chain structure.

Changes in myosin isozymes during development of chicken breast muscle.

The patterns of myosin isozymes in embryonic and adult chicken pectoralis muscle were examined by electrophoresis in a non-denaturing gel system (pyrophosphate acrylamide gel electrophoresis), and both light chains and heavy chains of embryonic and adult myosin isozymes were compared. In pyrophosphate acrylamide gel electrophoresis, the predominant isozyme component in embryonic pectoralis myosin could be clearly distinguished from adult myosin isozymes. SDS-polyacrylamide gel electrophoresis indicated that the light chain composition of embryonic myosin was also different from that of adult myosin. The pattern of peptide fragments produced by myosin digestion with a-chymotrypsin differed significantly between embryonic and adult skeletal myosin. These results suggest that myosin in the embryonic pectoralis muscle is different in both light and heavy chain composition from myosin in the same adult tissue.

Contractile properties of two varieties of twitch muscle fibres in Xenopus laevis

The contractile properties of twitch muscle fibres in the iliofibularis muscle of Xenopus laevis with characteristic differences in light-microscopical appearance have been studied under isometric and isotonic conditions. Type 1 fibres (large, pale) have a short contraction time (tc), a shoulder in the relaxation phase, and a high twitch-tetanus ratio. In type 2 fibres (medium-to-large with abundant mitochondria and lipid droplets) tc is longer, half-relaxation time equals tc, and the twitch-tetanus is lower. The capillary density is about 4 times higher for type 2 than for type 1. Computer-fitted hyperbolic force-velocity curves gave the following Hill constants (20 degrees C) for type 1 (2) fibres: P0*/P0 1.03 (1.15), a/P0* 0.48 (0.26), b 3.51 (1.53) 10/s; extrapolated Vmax (0-0.8P0) was 7.60 (6.27) 10/s. Lowered temperature (10 degrees C) increases the curvature of the P-V relation in type 1 fibres, little effect was seen in type 2. Increased PCO2 depressed the isometric tension in both types; in type 1 fibres the P-V relation became less curved, in type 2 fibres no change in curvature was observed. The results suggest that type 1 and type 2 fibres might contain myosin isozymes with slightly different temperature- and pH-sensitivities.

Distribution and properties of myosin isozymes in developing avian and mammalian skeletal muscle fibers.

Isozymes of myosin have been localized with respect to individual fibers in differentiating skeletal muscles of the rat and chicken using immunocytochemistry. The myosin light chain pattern has been analyzed in the same muscles by two-dimensional PAGE. In the muscles of both species, the response to antibodies against fast and slow adult myosin is consistent with the speed of contraction of the muscle. During early development, when speed of contraction is slow in future fast and slow muscles, all the fibers react strongly with anti-slow as well as with anti-fast myosin. As adult contractile properties are acquired, the fibers react with antibodies specific for either fast or slow myosin, but few fibers react with both antibodies. The myosin light chain pattern slow shows a change with development: the initial light chains (LC) are principally of the fast type, LC1(f), and LC2(f), independent of whether the embryonic muscle is destined to become a fast or a slow muscle in the adult. The LC3(f), light chain does not appear in significant amounts until after birth, in agreement with earlier reports. The predominance of fast light chains during early stages of development is especially evident in the rat soleus and chicken ALD, both slow muscles, in which LC1(f), is gradually replaced by the slow light chain, LC1(s), as development proceeds. Other features of the light chain pattern include an "embryonic" light chain in fetal and neonatal muscles of the rat, as originally demonstrated by R.G. Whalen, G.S. Butler- Browne, and F. Gros. (1978. J. Mol. Biol. 126:415-431.); and the presence of approximately 10 percent slow light chains in embryonic pectoralis, a fast white muscle in the adult chicken. The response of differentiating muscle fibers to anti-slow myosin antibody cannot, however, be ascribed solely to the presence of slow light chains, since antibody specific for the slow heavy chain continues to react with all the fibers. We conclude that during early development, the myosin consists of a population of molecules in which the heavy chain can be associated with a fast, slow, or embryonic light chain. Biochemical analysis has shown that this embryonic heavy chain (or chains) is distinct from adult fast or slow myosin (R.G. Whalen, K. Schwartz, P. Bouveret, S.M. Sell, and F. Gros. 1979. Proc. Natl. Acad. Sci. U.S.A. 76:5197-5201. J.I. Rushbrook, and A. Stracher. 1979. Proc Natl. Acad. Sci. U.S.A. 76:4331-4334. P.A. Benfield, S. Lowey, and D.D. LeBlanc. 1981. Biophys. J. 33(2, Pt. 2):243a[Abstr.]). Embryonic myosin, therefore, constitutes a unique class of molecules, whose synthesis ceases before the muscle differentiates into an adult pattern of fiber types.

Thyroxine-induced redistribution of isoenzymes of rabbit ventricular myosin.

HomeCirculation ResearchVol. 50, No. 1Thyroxine-induced redistribution of isoenzymes of rabbit ventricular myosin. Free AccessAbstractPDF/EPUBAboutView PDFSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyRedditDiggEmail Jump toFree AccessAbstractPDF/EPUBThyroxine-induced redistribution of isoenzymes of rabbit ventricular myosin. A F Martin, E D Pagani and R J Solaro A F MartinA F Martin Search for more papers by this author , E D PaganiE D Pagani Search for more papers by this author and R J SolaroR J Solaro Search for more papers by this author Originally published1 Jan 1982https://doi.org/10.1161/01.RES.50.1.117Circulation Research. 1982;50:117–124 Previous Back to top Next FiguresReferencesRelatedDetailsCited BySata M, Sugiura S, Yamashita H, Momomura S and Serizawa T (1993) Dynamic interaction between cardiac myosin isoforms modifies velocity of actomyosin sliding in vitro., Circulation Research, 73:4, (696-704), Online publication date: 1-Oct-1993.Goto Y, Slinker B and LeWinter M (1990) Decreased contractile efficiency and increased nonmechanical energy cost in hyperthyroid rabbit heart. Relation between O2 consumption and systolic pressure-volume area or force-time integral., Circulation Research, 66:4, (999-1011), Online publication date: 1-Apr-1990.Josephson R, Spurgeon H and Lakatta E (1990) The hyperthyroid heart. An analysis of systolic and diastolic properties in single rat ventricular myocytes., Circulation Research, 66:3, (773-781), Online publication date: 1-Mar-1990.McAuliffe J, Gao L and Solaro R (1990) Changes in myofibrillar activation and troponin C Ca2+ binding associated with troponin T isoform switching in developing rabbit heart., Circulation Research, 66:5, (1204-1216), Online publication date: 1-May-1990.Shibata T, Hunter W and Sagawa K (1987) Dynamic stiffness of barium-contractured cardiac muscles with different speeds of contraction., Circulation Research, 60:5, (770-779), Online publication date: 1-May-1987.Effron M, Bhatnagar G, Spurgeon H, Ruaño-Arroyo G and Lakatta E (1987) Changes in myosin isoenzymes, ATPase activity, and contraction duration in rat cardiac muscle with aging can be modulated by thyroxine., Circulation Research, 60:2, (238-245), Online publication date: 1-Feb-1987.Poggesi C, Everts M, Polla B, Tanzi F and Reggiani C (1987) Influence of thyroid state on mechanical restitution of rat myocardium., Circulation Research, 60:1, (142-151), Online publication date: 1-Jan-1987.Horowits R and Winegrad S (1987) cAMP regulation of myosin ATPase activity in the maturing rat heart., Circulation Research, 61:6, (914-924), Online publication date: 1-Dec-1987.Winegrad S and Weisberg A (1987) Isozyme specific modification of myosin ATPase by cAMP in rat heart., Circulation Research, 60:3, (384-392), Online publication date: 1-Mar-1987.Nagai R, Pritzl N, Low R, Stirewalt W, Zak R, Alpert N and Litten R (1987) Myosin isozyme synthesis and mRNA levels in pressure-overloaded rabbit hearts., Circulation Research, 60:5, (692-699), Online publication date: 1-May-1987.Lema M, Pagani E, Shemin R and Julian F (1986) Myosin isozymes in rabbit and human smooth muscles., Circulation Research, 59:2, (115-123), Online publication date: 1-Aug-1986.Solaro R, Kumar P, Blanchard E and Martin A (1986) Differential effects of pH on calcium activation of myofilaments of adult and perinatal dog hearts. Evidence for developmental differences in thin filament regulation., Circulation Research, 58:5, (721-729), Online publication date: 1-May-1986.Sen S and Young D (1986) Role of sodium in modulation of myocardial hypertrophy in renal hypertensive rats., Hypertension, 8:10, (918-924), Online publication date: 1-Oct-1986.Litten R, Martin B, Buchthal R, Nagai R, Low R and Alpert N (1985) Heterogeneity of myosin isozyme content of rabbit heart., Circulation Research, 57:3, (406-414), Online publication date: 1-Sep-1985.Dechesne C, Léger J, Bouvagnet P, Mairhofer H and Léger J (1985) Local diversity of myosin expression in mammalian atrial muscles. Variations depending on age and thyroid state in the rat and the rabbit., Circulation Research, 57:5, (767-775), Online publication date: 1-Nov-1985.Pagani E and Julian F (1984) Rabbit papillary muscle myosin isozymes and the velocity of muscle shortening., Circulation Research, 54:5, (586-594), Online publication date: 1-May-1984.Gorza L, Mercadier J, Schwartz K, Thornell L, Sartore S and Schiaffino S (1984) Myosin types in the human heart. An immunofluorescence study of normal and hypertrophied atrial and ventricular myocardium., Circulation Research, 54:6, (694-702), Online publication date: 1-Jun-1984.Winegrad S (1984) Regulation of cardiac contractile proteins. Correlations between physiology and biochemistry., Circulation Research, 55:5, (565-574), Online publication date: 1-Nov-1984.Samuel J, Rappaport L, Mercadier J, Lompre A, Sartore S, Triban C, Schiaffino S and Schwartz K (1983) Distribution of myosin isozymes within single cardiac cells. An immunohistochemical study., Circulation Research, 52:2, (200-209), Online publication date: 1-Feb-1983.Weisberg A, Winegrad S, Tucker M and McClellan G (1982) Histochemical detection of specific isozymes of myosin in rat ventricular cells., Circulation Research, 51:6, (802-809), Online publication date: 1-Dec-1982. January 1, 1982Vol 50, Issue 1Article InformationMetrics Copyright © 1982 by American Heart Associationhttps://doi.org/10.1161/01.RES.50.1.117 Originally publishedJanuary 1, 1982 PDF download Advertisement

Modification of the rapidly reacting thiols of atrial and ventricular myosins. Evidence for structural variances around the SH-1 thiol of the two isozymes.

Environmental variances were noted around the rapidly reacting SH-1 thiol of ventricular versus atrial myosin, based on electron paramagnetic resonance studies. Further studies, in which either SH-1 or SH-1 + SH-2 thiols were modified with N-ethylmaleimide, indicated the importance of the SH-2 moiety of both isozymes for generation of tension, when analyzed as synthetic actomyosin threads. Comparative EPR studies showed that the spin label was more strongly immobilized when complexed to ventricular SH-1 thiol as compared to when it was complexed to atrial myosin. Likewise, addition of PPi, ATP or ADP created a greater mobility in the spin label when added to ventricular spin-labeled myosin as compared to that of atrial myosin. comparative studies of spin-labeled actomyosin versus myosin analyzed at different EPR power settings also demonstrated disparaties surrounding the SH-1 thiol between the two myosin isozymes.

Fast to slow transformation of fast muscles in response to long-term phasic stimulation

Indirect stimulation via the peroneus nerve, 60-Hz stimulus trains of 2.5 s duration, applied every 10 s for 5 weeks transformed rabbit fast-twitch extensor muscles to the slow type as judged by histochemistry, myosin ATPase activities, and electrophoresis on polyacrylamide gels. Electrophoresis of single fibers from the stimulated muscle under dissociating conditions showed the presence of both fast- and slow-type light chains within the same fiber; under nondissociating conditions the slow-type myosin isozyme predominated. Histological examination of the 5-week stimulated muscle showed no signs of regeneration ( de novo fiber formation), suggesting reprogramming of existing fibers. These experiments show that fast to slow transformation is produced not only by continuous stimulation at a low frequency but also stimulation by trains at a higher frequency, indicating that muscle fiber transformation depends more on the total activity rather than the pattern of stimulation.

Three myosin heavy-chain isozymes appear sequentially in rat muscle development.

Three different heavy-chain isozymes of myosin appear sequentially in rat muscle during the period from late gestation to about three weeks of age. In part these changes can be related to changes in innervation taking place during this period.

Isoenzymes of rabbit slow myosin

Pyrophosphate gel electrophoresis has been established as a sensitive and reliable method of resolving myosin isozymes. The existence of 3 isozymes of vertebrate fast myosin differing in their alkali light chain distribution is well documented. In order of increasing mobility they represent the (LCr)a(LC&, (LCr)(LC&(LCa) and (LC&(LC& species [1,2,3]. However, in rat ventricular myosin, where only one light chain is analogous to the alkali light chains of fast skeletal myosin, the isozymes differ with respect to the iso-forms of 2 distinct heavy chains [4,5]. Fast skeletal myosin isozymes differ in the heavy chain [6-91. In case of rabbit slow myosin no isozymes were distinguishable on pyrophosphate gel [IO]. The existence of 2 different light chains (LCI,,LCIb) analogous to the alkali light chains of fast myosin [ 111, and as reported here, the existence of 2 forms of slow subfragment-l (S-l) separated in pyrophosphate gel suggests the presence of the isozymes analogous to the fast myosin isozymes. On the basis of analysis in pyrophosphate gels of single fibers, some of which contain predominantly either LC,, or LCrb, there are at least 2 isozymes of rabbit slow myosin namely, (LC&(LC& and (LCrb)z(LC2)2 horndims.

Changes in myosin and myosin light chain kinase during myogenesis.

Myosins and myosin light chain kinases have been isolated from a cloned line of myoblasts (L5/A10) as this cell line undergoes differentiation toward adult muscle. At least three myosin isozymes were obtained during this developmental process. Initially a nonmuscle type of myosin was found in the myoblasts. The molecular weights of the myoblast light chains were 20 000 and 15 000. Myosin isolated from early myotubes had light chains with molecular weights of 20 000 and 19 500. Myosin isolated from myotubes which contained sarcomeres had light chains with molecular weights of 23 000, 18 500, and 16 000. This last myosin was similar in light chain complement to adult rat thigh muscle. Two forms of the myosin light chain kinase activity were detected: a calcium-independent kinase in the myoblasts and a calcium-dependent kinase in the myotubes with sarcomeres. No myosin light chain kinase activity was detected in the early myotubes.

Studies on the amino groups of myosin ATPase: Trinitrophenylation of reactive lysyl residue in ventricular and atrial myosins

Myosin and heavy meromyosin from ventricular, atrial, and skeletal muscle were purified and trinitrophenylated by 2,4,6-trinitrobenzene sulfonate. The trinitrophenylation reaction followed a complex kinetics consisting of a fast and slow reaction in all preparations studied. Reactive lysine residues were trinitrophenylated during the fast reaction with a concomitant decrease in K + (EDTA)-activated ATPase and an increase in Mg 2+-stimulated ATPase activities of myosin. The extent of increase in Mg 2+-mediated ATPase was the highest with skeletal and the lowest with atrial myosin. The trinitrophenylation of the less reactive lysyl residues continued during the slow reaction. The rate constants of the reactions and the number of reactive lysine residues were evaluated by computer analyses of the trinitrophenylation curves. Two reactive lysine residues were found in skeletal and ventricular myosins while their number in atrial myosin was somewhat lower. The rate of trinitrophenylation in skeletal muscle myosin or heavy meromyosin was always higher than in the two cardiac myosin isozymes. Addition of KCl increased the trinitrophenylation of both highly reactive and slowly reactive lysyl residues in all of the three heavy meromyosins, however, the effect was more profound with cardiac heavy meromyosins. Addition of MgADP induced spectral changes in trinitrophenylated skeletal but not in cardiac myosins. Similar changes occurred in skeletal and to a lesser degree in ventricular heavy meromyosin, but no definite spectral changes were observed in atrial heavy meromyosin. The findings suggest that structural differences exist around the reactive lysyl residue in the head portion of the three myosins.

Changes in troponin-T and myosin isozymes during development of normal and dystrophic chicken muscles

Changes in troponin-T and myosin isozymes during development of normal and dystrophic chicken muscles

Cross-hybridization of light chains of cardiac myosin isozymes: Atrial and ventricular myosins

Cross-hybridization of light chains of cardiac myosin isozymes: Atrial and ventricular myosins

Transitions in contractile protein isozymes during muscle cell differentiation

The nature of the myosin synthesized in fused cultures of primary rat muscle cells and the myogenic cell line L6 was investigated. The myosin light chain subunits can be separated on two dimensional gels and the study of these proteins has led to the identification of a new form of light chain, called embryonic LC1 or LC1 emb (Whalen et al. (1978) J. Mol. Biol., 126 , 415–431). The relative rates of synthesis of the adult LC1 F and LC1 emb were measured during the several days following cell fusion. Although LC1 emb is the predominant Lc1 species synthesized two days after cell fusion, an evolution occurs such that by six days after fusion the synthesis of LC1 F is predominant. This result suggests that during normal differentiation myotubes exist which contain a myosin isozyme whose light chain composition is LC1 emb + LC2 F . Myotubes formed by L6 cells are unique in that they do not synthesize any significant amounts of LC1 F . These myotubes may thus represent the embryonic phase of development with respect to the light chains. The myosin heavy chain aggregates during isoelectric focusing and thus no qualitative information can be obtained concerning its nature using two dimensional gels. However, after partial chymotryptic digestion of SDS denatured myosin, a number of large polypeptides are obtained which can be conveniently separated on two dimensional gels. In this way it was shown that the L6 myosin heavy chain is a different isozyme when compared to adult fast and slow myosin heavy chains. Thus L6 cells harbor a heavy chain isozyme which may be of an embryonic type.

An Electrophoretic Study of Native Myosin Isozymes and of Their Subunit Content

Myosin polymorphism in muscles has been studied by a variety of electrophoretic techniques, in non-dissociating and in dissociating conditions. The analysis of myosin isozymes in the native state was achieved in pyrophosphate buffer and required only minute amounts of protein; identical results were obtained with purified or crudely extracted myosin. The determination of the subunit content of each isozyme was done in the presence of sodium dodecyl sulphate or urea for light chain, and in a phenol, acetic acid and urea system for heavy chain screening. Electrophoresis in non-dissociating conditions has led to the separation of up to a dozen of myosin isozymes, differing in mobilities by as much as 30%. Muscle specificity of myosin was clearly established. Apart from a few exceptions, all the muscles tested were shown to contain more than one myosin species; fast-twitch muscles for instance all contained the same three isozymes, but in variable ratios. Class specificity of myosin appeared related to the relative proportions of isozymes in a given muscle. A second electrophoresis in dissociating solvents of the myosin bands first resolved in pyrophosphate buffer has then allowed a further characterization of the various isozymes. The differences in mobilities observed in the native state were shown to come either from the light chains, or from the heavy chains, or from both. The first case was illustrated by the three species present in fast muscles, which were shown to correspond to three alkali light-chain isozymes, the heterodimer representing in some instances up to 40% of the total. Next to light-chain muscle type specificity, electrophoresis in the phenol, acetic acid, urea system has led to the detection of differences in the heavy chains of fast, slow and cardiac myosins. The application of these various electrophoretic techniques to the analysis of the modification of myosin isozymes during development or in pathology studies can be considered.

Fast and slow muscles in tissue culture synthesise only fast myosin.

ADULT fast and slow skeletal muscle fibres contain different myosins, a result of innervation by different classes of motoneurones1; innervation of one fibre type by the opposite motoneurone type leads to a switch in the kind of myosin synthesised2,3 within pre-existing fibres4,5. In embryonic muscles, however, the particular myosin isozyme synthesised before and during the early stages of innervation has been a subject of controversy. Some investigators claim that all embryonic muscle fibres—whether destined to be fast or slow in the adult—initially synthesise both ftast and slow myosins6,7. Proper innervation would then lead to a selection of one myosin type and repression of the other type within each cell. Others propose that the myosin of embryonic muscles is a distinct myosin, unique to the embryo8,9. On the other hand, we have presented evidence that all fetal muscles have an intrinsic programme which causes them to synthesise fast myosin initially10,11. After innervation, fast muscles continue synthesising fast myosin, while slow muscles switch to the synthesis of slow myosin. Some studies have corroborated our findings12–14, but in all these studies the earliest fast and slow muscles that could be obtained were already innervated, and the slow muscles already contained a small amount of slow myosin. Accordingly, to examine the initial miyosin synthesised in both fast and slow muscles before innervation, we have cultured tissue from chicken muscles destined to be fast or slow muscles in the adult. Muscle fibres in tissue culture are formed in the complete absence of innervation. Whether established from presumptive fast or presumptive slow muscles, all fibres in culture synthesised only fast myosin heavy and light chains.

Thyroid hormone stimulates synthesis of a cardiac myosin isozyme. Comparison of the two-two-dimensional electrophoretic patterns of the cyanogen bromide peptides of cardiac myosin heavy chains from euthyroid and thyrotoxic rabbits.

The CNBr peptides of [14C]carboxymethylated cardiac myosin heavy chains from euthyroid and thyrotoxic rabbits have been compared using a two-dimensional electrophoretic system. The results indicated that there were extensive differences in the peptide "maps" of these heavy chains, which included differences in the distribution of radiolabeled thiol peptides. Also, the patterns of heavy chain peptides from the cardiac myosins have been compared with those produced by the heavy chain myosin isozymes from skeletal muscles. Peptide maps of heavy chains from red skeletal muscle myosin closely resembled the pattern of peptides found with cardiac myosin heavy chains from euthyroid rabbits. However, peptide maps of heavy chains from white skeletal muscle myosin were dissimilar to those of the cardiac myosin isozymes. We conclude that thyroxine administration stimulates the synthesis of a cardiac myosin isozyme with a heavy chain primary structure which is different from either of the skeletal muscle myosin isozymes.

Thyroid hormone stimulates synthesis of a cardiac myosin isozyme

Thyroid hormone stimulates synthesis of a cardiac myosin isozyme