BIOCHEMICAL ARCHITECTURE 9 



birefringence of the preparations. Ultracentrifugation separates 

 two types of myosin A and B (= a, ^, Godeaux, 1954) and these 

 are somewhat contaminated by tropomyosin A. The amount of 

 myosin A (a) is increased and that of myosin B (p) decreased, by 

 the addition of ATP. Myosin B shows typical ATP-ase properties 

 and calcium ions act as a co-factor. Tropomyosin A has been 



Fig. 2. Electrophoretic pattern, pH 7-45, of the body wall of 



L. terrestris ; E = erythrocruorin ; a and /3 = myosins ; mi and m2 = 



albumens (from Godeaux, 1954). 



demonstrated by Kominz, Saad and Laki (1957), and filaments 

 resembHng paramyosin by Hanson and Lowy (1960). 



Flow birefringence measurements reveal that the molecular 

 length of myosin B is 1 •3-0*6 ^ in the absence of ATP, and 0-64- 

 0-43 IX in the presence of ATP and this is shorter than the length 

 obtained from striated muscles of insects. Myosin A, on the other 



