1765 



Szent-Gyorgyi, Albert. 1965. 



Cell division and cancer. Science 149(3679): 34-37. 



This is an important paper in that it traces the author's early interest and 

 work with biologically active substances. It refers only indirectly to work 

 on Mercenaria mercenaria. Reports discovery of 2 antagonistic substances, 

 one of which retarded and one of which promoted growth. The retarder was 

 named "retine" and the promoter "promine" . Despite their opposing effects 

 they were found to be very similar physically and chemically, almost the 

 same substance. Variability in behavior was later explained by work with 

 retine which showed that the substance has a very small molecule and is 

 bound in vivo to a hydrophilic colloid, from which, it can be released 

 fairly easily. Bound to its carrier retine is stable; released, it is 

 unstable. The relation of the 2 substances to cancer offers some intriguing 

 research possibilities. - J.L.M. 



1766 



Szent-Gyorgyi, Andrew G. 1953. 



Meromyosins, the subunits of myosin. Arch. Biochem. Biophys. 42(2): 305-320. 



Short digestion of myosin by trypsin produced 2 subunits L-meromyosin , 

 with molecular weight 96,000 and 550A long and 16A wide; and H-meromyosin, 

 with molecular weight 232,000 and 435A long and 29A wide. H-meromyosin has 

 the total ATPase activity and the capacity to combine with actin of the 

 intact myosin molecule. One myosin molecule consists of 4 L-meromyosins and 

 2 H-meromyosin molecules. It is proposed that the L-meromyosin molecules 

 are linked in a chain and the H-meromyosins are attached to them. It is 

 suggested that L-meromyosin is the contractile part of the myosin molecule. 

 Mercenaria (Venus) mercenaria is not mentioned. - J.L.M. and M.W.S. 



1767 



Szent-Gyorgyi, Andrew G., Carolyn Cohen, and John Kendrick-Jones. 1971. 



Paramyosin and the filaments of molluscan "catch" muscles. II. Native 

 filaments: Isolation and characterization. J. Mol , Biol. 56C2): 239-258. 



A new method for partial separation of the filaments of molluscan muscles 

 produces 2 fractions, one mainly of actin filaments, many of which were 

 attached to dense bodies, and one consisting of very long and thick filaments 

 which contained essentially all the paramyosin and myosin in the muscle. 

 Some actin filaments also were present in the 2nd fraction. When solution of 

 myosin was prevented, myosin filaments similar to those of vertebrate 

 striated muscle seldom were found in either fraction. Myosin could be 

 extracted selectively from thick filaments without solution of paramyosin, 

 but extraction of paramyosin was always accompanied by solution of myosin. 

 Removal of myosin changed the surface appearance of thick filaments: a 

 characteristic pattern of darkly staining nodes or gap regions in the 

 paramyosin filament was visible in negatively stained preparations. Nodes 

 were roughly triangular, defining polarity of the structure. Some filaments 

 showed reversal of polarity along their length. It was concluded that thick 

 filaments have a bipolar core of paramyosin covered with a surface layer of 

 myosin. Molluscan myosin (including that of Mercenaria mercenaria) formed 

 filaments resembling those of rabbit myosin when precipitated in vitro. Its 

 assembly in the thick filament therefore is determined by the paramyosin core. 

 Paramyosin greatly inhibited actin-activated ATPase of myosin selectively when 

 these proteins were mixed about mole to mole. Long bipolar thick filaments 

 with myosin on the surface can explain the development of tension in these 

 molluscan muscles according to the sliding filament theory. This suggests 

 also that paramyosin may have a specific regulatory role in tension 

 maintenance: in the catch mechanism a phase change in paramyosin may be 

 coupled to movement of cross-bridges formed between myosin and actin. - 

 modified authors' abstract - J.L.M. 



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