56 W. F. H. M. MOMMAERTS VOL. 4 (1950) 



might likewise be caused by the binding of ATP by myosin followed by phosphorylation 

 of the latter. On this point therefore, no decision seems possible as yet. 



With respect to the moment at which the energy of metabolism is made available 

 to the contractile apparatus, it is now customary (see-'') to distinguish two possible 

 mechanisms. In the first of these, chemical energy may be transferred at the very mo- 

 ment of contraction, when it is necessary. The alternative possibility is that the primary 

 event merely releases, by a trigger action, a spontaneous contractile process (often 

 paralleled with the shortening of stretched rubber), and that it is the event of relaxation 

 which is linked with exergonic m.etabolic reactions in order to restore the active state. 

 The latter category, the so called postenergization mechanisms, seems difficult to recon- 

 cile with the results of Fenn and Hill^^, is indicating rather the existence of contraction- 

 coupling. Nevertheless, postenergization hypotheses are rather in demand at present, 

 and the opinion seems to prevail that Szent-Gyorgyi's work may lead to this type of 

 inter probation, a viewpoint taken, e.g., in the speculations of Morales^^. As the present 

 communication shows, the analysis of the effects discovered by Szent-Gyorgyi gives, 

 on the contrary, rise to a preenergizationtheory. 



It has been the purpose of this discussion to show where the actual experimental 

 analysis of the contractile event, in terms of ATP-actomyosin interaction, at present 

 stands. No detailed theory seems warranted, or, as Meyerhof said in 1930^^ (p. 280) : 

 "Es soil daher hier weniger eine bestimmte Theorie ausgearbeitet werden als die fest- 

 gestellten Tatsachen und die sich daraus ergebenden mehr oder weniger wahrschein- 

 lichen Folgerungen zusammengefasst sowie Missverstandnisse gegeniiber der Auslegung 

 dieses Tatbestandes beseitigt werden". But neither should the impression prevail 

 that "... (man) auch heute eigentlich noch gar nichts weiss". 



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