Protein Complexes as Biochemically Active Systems 



475 



substrate hydrolysis. Similar data were obtained by us for the proteolysis by 

 trypsin and by its complex with ergosterol of heat-denatured egg albumin and 

 of casein. 



Special experiments have been carried out in order to study the changes in 

 proteolysis of serum albumin by another proteolytic enzyme, viz. pepsin, as 

 dependent on whether pepsin is free or forms a complex with ergosterol. The 



2 3 



hn 



Fig. 4. The kinetic curves for serum albumin proteolysis by trypsin (I) and by 

 its complex with ergosterol (II) determined by Van Slyke's method. 



Table i 



Activity of trypsin and trypsin-ergosterol complex as a function of 

 enzyme amount 



(Determined at 400 mix — see text) 



results of the experiments, in which the same procedure was used as in trypsin 

 experiments (enzyme/substrate ratio 1/500 and i/iooo), showed that with the 

 pepsin-ergosterol complex proteolysis proceeds at a much higher rate than with 

 pepsin alone). 



It is concluded, therefore, that the course of proteolysis is changed by the 

 interaction of the enzyme protein with lipid substances. In our view [28], these 

 results indicate that the formation and breakdown of protein-hpid complexes 

 is one of the possible tools for controlling enzymic processes going on within 

 the organism. 



