雑誌目次

　Although "myosin B，" the isolable contractile substance of muscle, has been the object of worldwide study, its nature remains controversial．By most workers it is thought to be a compound of myosin（or "myosin A"）and actin-formable by combination of actin and myosin, and dissociable (［KCl］≧．5) upon addition of ATP．But a few workers have not agreed with all features of this hypothesis．For example, Tsao's observations on the rotaional relaxation time of actin in the presence of myosin were considered by him to be incompatible with assuming that actin forms a compound with myosin（1）．

　The studies initiated in Szent-Györgyi's laboratory（1）have clearly established that the fibrous muscle protein known in the early literature as myosin, as myosin-B of the Szeged-group, consists of two proteins, viz．myosin proper（L-myosin of Weber）and F-actin, and, subsequently, the more appropriate term actomyosin was adopted to denote the complex．It is obtainable not only by direct extraction from muscle by slightly alkaline salt solutions of fairly high ionic strength（natural actomyosin）but it can also be reconstituted from purified myosin and F-actin．

　INTRODUCTION
　The interaction between actomyosin and ATP, i. e.，the size and shape change of actomyosin particle with ATP and the hydrolytic dephosphorylation of ATP catalyzed by the protein, has long been investigated by many workers, such as Morales et al.（1, 2），Mommaerts（3, 4），Tsao（5）and Gergely（6）．This laboratory has also devoted more than six years to studies on the physicochemical and enzymic properties of myosin B, the results of which were reported in a review（7）in some detail．

　INTRODUCTION
　Many reactions of biological significance involve the consumption or production of H^＋ ions．Since these reactions proceed at constant pH, they are "coupled" with reactions in which H^＋ is either removed from the acidic member of the buffer pair or is absorbed by the basic member．

　Some time ago it was found that ethylenediaminetetraacetate（EDTA）increases the ATP-ase activity of myosin at higher salt concentrations（1）．In the work reported here, the myosin B ATP-ase activity has been studied over a range of ATP and EDTA concentrations, and the data have then been examined in terms of various kinetic schemes．

　The fact that myosin ATPase has two optimal values of pH was discovered first by Engelhardt and Ljubimova in 1942（1）．They suggested that these pH optima might be explained by the ionization of the enzyme and the ionization of the substrate（1）．
　On the other hand, it was observed by Mehl（2）that myosin ATPase is inhibited reversibly by the treatment of hydrogen peroxide in alkali range．Then he considered that this phenomenon is resulted from the coexistence of two enzymes in his sample．And he attempted to separate these enzymes but was unable to achieve success．Recently, Mommaerts et al．

　Actomyosin, the contractile protein in muscle, undergoes remarkable change in its shape by ATP and, at the same time, possesses the enzymatic activity which catalyses the hydrolysis of end group of ATP（1〜3）．The interaction between ATP and actomyosin has been studied by many investigators in order to obtain the information of mechanism of muscular contraction（4〜8）．
　The recent tendency in the biochemistry of muscle is to consider the enzymatic hydrolysis of ATP as the energy-yielding reaction of muscular activity, but it is not yet clear how the physical change of actomyosin is caused．

　I．INTRODUCTION
　The current biochemical theories of muscular contraction are chiefly based upon a number of fruitful investigations on rabbit skeletal muscle．It is of great interest to conduct comparative studies in the animal kingdom on a wide scale．The results may be useful to decide what phenomena are essential for muscular function, because the essential events must be universal among all animal muscles．
　For the last five years, the writer has been engaged in the comparative biochemistry of muscle contractile proteins in invertebrates．The outline of the study has been recently summed up（1）．

　INTRODUCTION
　Physico-chemical studies on actin have been made by many authors（1〜8）．No decisive conclusions, however, have yet been obtained on the state of actin molecules in solutions and on the mechanism of their g-f transformation．F-actin is considered to be fibrous aggregates of globular actin molecules；but various experimental methods, for example, measurements of light scattering and flow birefringence, give different results for estimation of the length of f-actin units（4〜6）．

　Although much is known concerning the comparative amino acid composition of purified proteins in mammals, less is known about lower vertebrates and very little about invertebrates（1, 2）. A major difficulty in comparative studies is the selection of a protein that is present throughout the animal kingdom. All animals possess locomotion or motility, and, except for those which depend exclusively on cilia or flagellae for motion, muscle tissue is the common instrument of movement. Therefore, a purified muscle protein would appear to be suitable for comparative studies.

　When trypsin or chymotrypsin acts on myosin, two kinds of fragments（3 pieces/ mole），the so-called meromyosins are produced（1〜5）. It was found by A. G. Szent-Györgyi that when alcohol denaturation is applied to L-meromyosin about 60％ of it remained undenatured and crystallized in needles（6）.
　In the experiment reported here a reverse approach was tried. The myosin was first denatured by a procedure similar to that used by Szent-Györgyi to denature L-meromyosin（7）.

　It is now generally accepted that the system actin, myosin and adenosinetriphosphate contains the essential components of the contractile mechanism of muscle. In spite of the efforts of dozens of investigators working through nearly two decades, the nature of the interaction of the three remains a source of fascination as well as a challenge to all who are interested in the problem of the chemistry of muscle contraction.
　The present communication is not concerned with this system, and in a sense it might be unrelated to the central theme of the Conference.

　RELAXATION WITH PHOSPHOENOLPYRUVATE
　Rabbit psoas fibers kept initially at 0℃ in 50％ glycerol for two days and extracted further in 20％ glycerol at 20℃ for 4〜8 hours, develop maximal isometric tension on addition of 4 mM adenosinetriphosphate（ATP），and no appreciable spontaneous relaxation follows．According to recent work from this laboratory（1, 2），however, immediate relaxation of these fibers can be obtained if mM phosphoenolpyruvate（PEP）is added．

　INTRODUCTION
　Bozler（1）has shown that the high concentration of ATP could produce the relaxation of freshly glycerinated muscle fibers shortened by the low concentration of ATP．Later, Bendall（2）introduced the Marsh factor（3）into the experiment of muscle model and succeeded in demonstrating a contraction-relaxation cycle of glycerinated muscle fibers by using the physiological concentration of ATP．

　The relaxing effect of EDTA（Ethylenediamine-tetraacetic acid）on the glyceroltreated fiber of rabbit psoas muscle has been studied by the isotonic kymography under the load of 100 to 400 grams per cm² of the cross section area of fiber（1, 2）．
　To be more quantitative, the isometric method^1） has been used in this paper．Two kinds of observation shall be presented here； one suggests the relatively small number of active sites for contraction and the other is concerned with the SH-group．

　Even though ATP-actomyosin reaction in various kinds of muscle has been fully demonstrated, it might be considered, that there are physiological and chemical discrepancies between the very primitive muscle of lower animals and a mechanism of highest precision such as the skeletal muscle of a mammalian．Thus the question arises, what kind of device might be acquired in the muscle as a consequence of the development of the organism．

　It is generally known today that glycer inated-muscle fibers are contracted by the addition of adenosinetriphosphate（ATP）and at the same time they dephosphorylate the ATP．But, in this inhomogeneous system, the relation between the mechanical changes and chemical reaction are not sufficiently understood．From the experiments of free contraction of the fiber reported by Mugikura（1）or Bowen and Kerwin（2）, it will be accepted that the rate of dephosphorylation reaches its steady value far before the contraction height reaches its stationary value．

　In Verbindung mit der Untersuchung der Muskelfunktion ist es eine seit langen umstrittene Frage, welches der primäre energieliefernde Prozess der Muskelfunktion sei und auf welche Weise die Struktureiweisse des Muskels am Kontraktionsprozess teilnehmen，d．h．ob diesen Eiweissen in den einzelnen Stufen der Kontraktion und Relaxation zustande kommen und wie sich während der Kontraktion die Struktureiweisse verändern．Diese beide Fragen hängen miteinander zusammen, und es wird angenommen, dass in diesem Prozess dem Aktomyosin eine Rolle zufällt（1, 2）．

　From a physiological point of view, some fundamental problems about the metabolic processes in living muscle as an important factor which modifies the actomyosin-ATP reactions, remain still to be solved, including that of the excitatory processes.
　Some observations about the changes of the rate of respiration during muscular shortening will be presented in this brief comment.

　The liberation of ions and changes of metabolism in sartorius muscle of frog (and of toad) were studied in various unphysiological media. The results were discussed in relation to loss of excitability especially in the case of the isotonic glucose solution which showed an interesting peculiarity.

　I
　The theory concerning the mechanism of muscular contraction which is upheld by the majority of research workers along this line is as follows； the filament of myofibrils is made up from Actomyosin（or Actin plus myosin）, and this contracts by ATP and extends by the relaxation factor．
　However, since this theory has its basis upon the experimental results concerning the substance extracted from the muscle or the glycerol muscle, there still remains several problems to be clarified in order to fully explain the contraction process of the living muscle．

　Smooth muscle shows some interesting characteristics in its form and function．Under a light microscope, the smooth muscle，as it is named, has no particular pattern．In some animals, however, it shows oblique striations or fibrillar structures．
　The electron microscope reveals the detailed structure in the smooth muscle as well as in the striated muscle．There are many different kinds of structures in the smooth muscle．

　I wish to thank you for the opportunity which you gave us to come to your meeting and have a talk with you here．We regret very much not to have been able to come to the Conference which, as I have heard from many guests from abroad, was a great success；we see from the proceedings that a great number of very important people reported there, so we have lost much by not being able to be present．We must make our excuses for coming to the present meeting completely unprepared．We have not been able to prepare anything reasonable beforehand so it will be almost a kind of improvisation．

　Ferdman and Nechiporenko（1946）expressed the view that myosin possesses the property to deaminate ATP and AMP．Attention was thus drawn again to Embden's claims that the principal chemical reaction underlying muscular contraction is alkalinization of the tissuea concept opposed by Meyerhof and Parnas．The shift of reaction would be the result of deaminase activity．This controversy was resolved in favour of Meyerhof and Parnas, while Embden's concept has gradually become obsolete．The abovementioned statements of Ferdman and Nechiporenko led to a reconsideration of the problem．