The alpha- and beta-subunits of membrane-bound ATP synthase complex bind ATP and ADP: beta contributes to catalytic sites, and alpha may be involved in regulation of ATP synthase activity. The sequences of beta-subunits are highly conserved in Escherichia coli and bovine mitochondria. Also alpha and beta are weakly homologous to each other throughout most of their amino acid sequences, suggesting that they have common functions in catalysis. Related sequences in both alpha and beta and in other enzymes that bind ATP or ADP in catalysis, notably myosin, phosphofructokinase, and adenylate kinase, help to identify regions contributing to an adenine nucleotide binding fold in both ATP synthase subunits.

Distantly related sequences in the alpha- and beta-subunits of ATP synthase, myosin, kinases and other ATP-requiring enzymes and a common nucleotide binding fold.

Directed movement is a characteristic of many living organisms and occurs as a result of the transformation of chemical energy into mechanical energy. Myosin is one of three families of molecular motors that are responsible for cellular motility. The three-dimensional structure of the head portion of myosin, or subfragment-1, which contains both the actin and nucleotide binding sites, is described. This structure of a molecular motor was determined by single crystal x-ray diffraction. The data provide a structural framework for understanding the molecular basis of motility.

https://science.sciencemag.org/content/sci/261/5117/50.full.pdf

Three-dimensional structure of myosin subfragment-1: a molecular motor

Introduction. ............................................................ 129 Fiber Types. ............................................................ 130 Historical introduction. ................................................. 130 Classification and terminology. ........................................... 131 Contractile properties of different types of fiber. ............................ 134 Mechanical Properties. .................................................... 138 Introduction ........................................................... 138 Series-elastic component. ................................................ 138 Length : tension relation of contractile material. ............................. 140 Force: velocity properties of contractile component. ......................... 145 Behavior of series-elastic and contractile components in isotonic and isometric contractions ....................................................... 147 Active state, time course of isometric twitch, and posttetanic potentiation ....... 149 Ontogenetic Differentiation of Fast and Slow Muscles. ......................... 161 Growth ............................................................... 161 Dynamic properties. .................................................... 163 Other developmental changes. .......................................... 166 Kelation Between Size and Speed of Contraction .............................. 166 Speed of contraction of homologous muscles of different species. ............. 166 Speed of contraction of different muscles of same animal. .................... 169 Neural Control of Dynamic Properties. ...................................... 170 Introductiorl ........................................................... 170 Dynamic properties of normal and cross-innervated muscles .................. 172 Effects of nerve cross-union on properties of myosin. ......................... 175 Neural influences on noncontractile structures in muscle cells ................. 176 Correlations Between Dynamic and Chemical Properties of Contractile Material. .. 177 Introduction ........................................................... 177 Structure of myosin. .................................................... 177 Relation between ATPase activity of myosin and intrinsic speed of shortening . 181 Functional differences between fast and slow muscles. ....................... 182 Review of Some Major Problems ........................................... 183

Dynamic properties of mammalian skeletal muscles.

Muscle contraction consists of a cyclical interaction between myosin and actin driven by the concomitant hydrolysis of adenosine triphosphate (ATP). A model for the rigor complex of F actin and the myosin head was obtained by combining the molecular structures of the individual proteins with the low-resolution electron density maps of the complex derived by cryo-electron microscopy and image analysis. The spatial relation between the ATP binding pocket on myosin and the major contact area on actin suggests a working hypothesis for the crossbridge cycle that is consistent with previous independent structural and biochemical studies.

https://science.sciencemag.org/content/sci/261/5117/58.full.pdf

Structure of the actin-myosin complex and its implications for muscle contraction.

Publisher Summary Ca release from the sarcoplasmic reticulum (SR) is one of the most important steps in excitation–contraction coupling of skeletal muscle. This chapter describes the physiological release of Ca from the SR, various modes of Ca release from the SR, and the physiological significance of various Ca release mechanisms. Ca ion is the mediator of information of action potentials to the contractile machinery; however, the physiological source of the mediator Ca is not yet unequivocally established. The inhibitors of Ca-induced Ca release––procaine and adenine––were shown not to inhibit contraction of living skeletal muscle fibers induced by the depolarization of the surface membrane. Studies of the ionic composition of the lumen of the SR by electron-probe analysis show that there are no significant differences between the ionic compositions in the lumen of the SR and that in the cytoplasm except for Ca ion. The essential part of the physiological Ca release mechanism is almost entirely unknown; therefore, further studies, especially by using preparations, such as improved cut fibers, that retain the physiological tubule (T)–SR coupling mechanism, but have easy access to sarcoplasm so that its composition can be altered at will, are necessary.

Calcium release from the sarcoplasmic reticulum

Purified preparations of rabbit skeletal white, red, and cardiac muscle myosin (WM, RM, and CM) were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Significant differences in both the molecular weights and number of light chains in these myosins were found. WM has three distinct light-chain components (LC1W, LC2W, LC3W) having molecular weights of 25,500, 17,400, and 15,100, respectively. No component with a molecular weight around 15,000 is present in RM or CM. RM and CM contain components of identical molecular weights close to 25,000 and 17,000 (LC1CR and LC2CR) which, however, clearly differ in molecular weight from the corresponding subunits in WM. RM has an additional component (LC1R) having a slightly higher molecular weight than LC1W and LC1CR. Thus differences and similarities in many biochemical properties between WM, RM, and CM, which have been described earlier, are also reflected in the light-chain components. The present results support the hypothesis that different sets of genes are active in producing components of myosin that make up different isozymic forms characteristic of each muscle type.

Light Chains of Myosins from White, Red, and Cardiac Muscles

Location of SH-1 and SH-2 in the heavy chain segment of heavy meromyosin.

Continuous stimulation of a rabbit fast muscle at 10 Hz changes its physiological and biochemical parameters to those of a slow muscle. These transformations include the replacement of myosin of one type by myosin of another type. Two hypotheses could explain the cellular basis of these changes. First, if fibers were permanently programmed to be fast or slow, but not both, a change from one muscle type to another would involve atrophy of one fiber type accompanied by de novo appearance of the other type. Alternatively, preexisting muscle fibers could be changing from the expression of one set of genes to the expression of another. Fluorescein-labeled antibodies against fast (AF) and slow (AS) muscle myosins of rabbits have been prepared by procedures originally applied to chicken muscle. In the unstimulated fast peroneus longus muscle, most fibers stained only with AF; a small percentage stained only with AS; and no fibers stained with both antibodies. In stimulated muscles, most fibers stained with both AF and AS; with increasing time of stimulation, there was a progressive decrease in staining intensity with AF and a progressive increase in staining intensity with AS within the same fibers. These results are consistent with a theory that individual preexisting muscle fibers can actually switch from the synthesis of fast myosin to the synthesis of slow myosin.

/pdf/use-of-type-specific-antimyosins-to-demonstrate-the-3g44p7er0u.pdf

Frank A. Sreter

Papers

Light Chains of Myosins from White, Red, and Cardiac Muscles

Location of SH-1 and SH-2 in the heavy chain segment of heavy meromyosin.

Use of type-specific antimyosins to demonstrate the transformation of individual fibers in chronically stimulated rabbit fast muscles.

Structural and functional changes of myosin during development: comparison with adult fast, slow and cardiac myosin.

Temperature, pH and seasonal dependence of Ca-uptake and ATPase activity of white and red muscle microsomes.