DUGALD E. S. BROWN 



107 



The glycerated fiber systems differ from muscle in that the activator, 

 such as pH or calcium, is under the control of the investigator whereas 

 in muscle the production of the activator is a consequence of the depolari- 

 zation of the cell. The alpha process, described in the high pressure studies, 

 is considered to depend on the time course of the activator cycle. Experi- 

 mentally it is measured in terms of tension which, however, merely re- 

 flects the activation charge set up at the beginning of the contraction. 

 In the auricular muscle of the turtle it turns out that the formation of 

 the activated contractile complex as the result of a stimulus proceeds 

 with a reduction in volume of 720 cc/mole. In relation to other events 

 in contraction, this large volume decrease occurs coincidentally with the 

 latency relaxation and the development of the 'active state.' In terms 

 of the schema below, the very large volume reduction is considered to 

 arise from a situation in which each mole of activator catalyzes the 

 formation of two activated units, each unit being activated undergoing 

 a reduction in volume of 360 cc/mole or 120 cc/mole per active site. 



-E 

 AMi 



rE 



-E (A) 



AV = -360 



rE* 



E* 



^E* 



AMi + 



(D) 



AV = +180 

 AH = 36,000 



-P 



-P 



P 



AMar 



AV = 



+ 120 



(B) 



contraction 



AM 



P 

 P 

 P 



(G) 



In the preceding it has been considered that the activator reaction (A) 

 and the phosjihorylating reaction (D) are necesary for the formation and 

 contraction of the activated unit. In such a system the activation charge 

 would be proportional to the number of activated units produced by 

 reaction (A) and also to the phosphate potential per unit as set by 

 reaction (D). Referring to the schema, reaction (A) proceeds with a 

 decrease in volume of 360 cc/mole and is augmented by pressure, while 

 reaction (D) jiroceeds with an increase in volume of 180 cc/mole and is 

 inhibited by jiressure. It is clear from the opposite signs of the aV 

 ^'alues that the reactions are cjuite different. The difference is further 

 borne out by the fact that the activation requires time to build up and is 

 governed by a rate equation. It may be supposed that reaction (A), 



