Protein Complexes as Biochemically Active Systems 



473 



of the isotherms of trypsin compressibility in a monolayer on 5% ammonium 

 sulphate solution. Fig. i gives curves for the dependence of the surface pressure 

 F on the product FA in a unimolecular layer for trypsin (curve I) and for the 

 trypsin-ergosterol complex (curve II). These curves [26] indicate that the mole- 

 cular weight of trypsin in the monolayer, as calculated according to the equation 

 of ideal gases from the length of the section ß between the intersections of the 

 curves with the FA axis, equals 40,000 for trypsin and 80,000 for its complex 

 with ergosterol. Thus just as in the case of egg albumin, trypsin, in forming a 

 complex with ergosterol, produces associates detectable in the monolayer. 

 Special experiments revealed that this complex is maintained during 48 hours 

 at a pH of 7-5-8-I. 



FA 



0-8 

 0-7 

 0-6 

 0-5 

 0-4 

 0-3 

 0-2 

 0-1 



O 



0-1 



0-2 



0-3 



F 



0-4 0-5 



0-6 



Fig. I. The dependence of the surface pressure F on the product FA in a 

 monomolecular layer for trypsin (I) and for the trypsin-ergosterol complex (II). 



The proteolytic activity of trypsin was determined spectrophotometrically 

 according to the Kunitz method [27] at 280 m/x and according to a modified 

 Kunitz method at 400 m/n, as well as by determining the amino nitrogen in the 

 incubated sample according to Van Slyke's method after precipitation by tri- 

 chloroacetic acid. 



Fig. 2 gives curves for the digestion of serum albumin by trypsin (curve I) 

 and by the trypsin — ergosterol complex (curve II) as a function of the amount 

 of enzyme. Here the extinction at 280 m/x is plotted against the enzyme-substrate 

 ratio. It follows from these curves that the complex has a higher proteolytic 

 activity than pure trypsin, especially at enzyme/substrate ratios within the range 

 1/200-1/50. Table i Hsts the results of another experiment. In this case the 

 optical densities (Aiîi for trypsin and Ä£'2 for the complex) are obtained by 

 subtracting the optical density after 90 minutes of proteolysis from the optical 



