208 



FREDERICK G. E. PAUTARD 



' 



Fig. 8. Contraction of perch actomyosin with ATP. (a) Gel specimen 

 of perch actomyosin, prepared by acidification of dilute alkaline-salt ex- 

 tract of perch dorsal muscle. In buffered 0.1M KC1 solution (x50). (b) Gel 

 specimen shown at (a) 2 min after addition of ATP (0.003M approxi- 

 mately) and MgCl 2 (0.002M) in 0.1M KC1 solution, pH 7.0. Some parts of 

 the gel [encircled 1 in (a) and (£>)] have remained inert (x50). 



Fig. 8. The original gel, in buffered 0.1 A/ KC1, shown in Fig. 8a 

 shrank in 2 min to the contracted form shown in Fig. 8b. An impor- 

 tant feature of actomyosin-gel shrinkage that must be emphasized is 

 that syneresis does not take place either with uniform speed or with 

 uniform dimensional changes throughout the gel. Very frequently, 

 parts of the specimen do not contract at all (the portion of the gel 

 encircled 1 in Figs. 8a and 8b, for instance). This unequal shrinkage 



