52 MACROMOLECULAR COMPLEXES 



charge characteristics which are responsible for (a) the fact that several differ- 

 ent stable aggregation states can be formed under appropriate conditions (see 

 Hodge, 1959a, 1959b, for summaries) and (b) the sharpness of the various 

 band patterns. The presence of short sequences of polyglutamic acid in the 

 paramyosin macromolecule would be in accord with this concept, especially 

 since this is an a-type protein, in which such polar "clusters" must be formed 

 by the coiling of a single polypeptide chain; in the tropocollagen macro- 

 molecule, on the other hand, such polar "clusters" could result from the mutual 

 coiling of three separate polvpeptide chains, and the probability of finding 

 polypolar sequences would be less. 



Dr. Prosser (University of Illinois): I am still not clear regarding the 

 ATP effect on collagen polymerization. If it is a matter of charge distribution, 

 the polyanions should be effective. Is energy liberated? Is the ATP split? 



Dr. Hodge: The effect of ATP on the ordered aggregation of TC macro- 

 molecules is unquestionably a matter of charge distribution, and polyanions, 

 such as nucleic acid, are effective in inducing the formation of SLS-type struc- 

 tures. However, the system is rather delicately balanced with respect to pH 

 and ionic strength, so that the pK of the inducing agent is fairly critical. As far 

 as I know, SLS formation does not involve liberation of energy from splitting 

 of ATP. 



Dr. Sherman (Brown University): Is Mg++ required for the ATP effect? 



Dr. Hodge: Mg++ is not required for the formation of SLS-tvpe aggre- 

 gates, and indeed, would probably inhibit the precipitation because of its 

 relatively high contribution to the ionic strength of the medium. 



