May, 1946
FILMMOLECULAR WEIGHTOF MONOLAYERS OF @-LACTOGLOBULIN
urea solutions. In view of the small concentration of protein used, we regard this interpretation as unlikely. The apparent increase of the niolecular weights in i’ and in 8 M urea is undoubtedly due to progressive aggregation as. both solutiohs showed a degree of turbidity which was not present in the other urea concentrations used. Acknowledgment.-It is a. pleasure to acknowledge the generous support afforded this research by Corn Products Refining Co. of Argo, Illinois. We also wish to thank Drs. W. Heller and 11. B. KleL-ciis for their kind permission to use their uiipublished results on light scattering.
[ C O N T R I U I T I O N FROM TIIB
745
Summary 1. Twenty osmotic pressure measurenients on solutioiis of 8-lactoglobulin in 0.5 M sodium chloride have been reported. A molecular weight of 35,050 with a standard deviation of the mean of 144 has been calculated. 2. The osmotic pressure of @-lactoglobulin solutions in several concentrations of urea have been measured. I t is concluded that urea probably dissociates /3-!actoglobulin into two fragments. CHICAGO, ILLINOIS
RECEIVED13FEBRUARY 13, 1946
(13) Original mnnttscril,t receivcd June 23, 1945.
DEPARTMENT O F CHEMISTRY, NORTIIWBSTERN ITNIVERSI rY hI&DICALSCIIOOI.]
Monolayers of 0-Lactoglobulin. 11. Film Molecular Weight BY HENRYB. BULL 111a prcvious paper’ it was shown that @-lactoglobulin prepared from fresh, raw whole milk forms a gaseous iiionolaycr on the surface of concentrated aiiinioniuxii sulfate solutions and from the application of the gas laws in two dimensions, the niolecular weight along with the area of the gaseous molecules was calculated. The film molecular weight reported for 0-lactoglobulin was about 44,000 and the area of the gaseous film was 1.21 sq. meters per milligram of protein. Since that time, the molecular weight of 0-lactoglobulin has been determined by osmotic pressure measureinents2and found to be 35,050 with a standard deviation of the mean of 144. In view of this discrepancy bctween the results of these two tccliniqurs, it was tlccidcd to reinvestigate in grcatcr tlctail g:iseous spread filiiis of p-lactoglolxiliii 011 coiiccii tratctl : i i i i i i i o i i i r i i i i sulfatc solritioils. I t has i i o w I)ccii foitnti possihlc to rccoiicile the res111t.sfroin sutfaec lilm teclitiiclue aiid from osmotic I)rcssrirc iiic;isttrenietits. ’I’hesc. studies are reported it1 this paper. Experimental The 8-lactoglohuliii was prepared from fresh, raw whole milk by the tcchniquc tiescrihcd by Bull and Currie.2 The protciri was recrystallizecl scvcral times by dialyzing a sohitioil of thc protciii i i i 0.07 111 sodium chloridc against water. Thc lirotciiii crystals were dissolved i i i 1 Af sodium chloridc aiitl enough watcr added to rnakc tlic solutioii 0.5 i\f in respert to :
