34 MASS. EXPERnrENT STATION BULLETIN 374 



1. Inadequate saturation of the enzyme as substrate concentration 

 decreases. This factor may be ignored in these experiments as an ex- 

 planation for the effects of iodine, because there was an ample amount 

 of substrate present in the samples tested, as is shown by the unretarded 

 enzyme activity in the control samples. 



2. Reversible union of part of the enzyme with reaction products or 

 with the substrate to form an inactive compound, or irreversible destruc- 

 tion of the enzyme. Thus, the depression of the activity of an enzyme 

 may be either a reversible or an irreversible change. 



Haldane (6) made the statement that all enzymes so far investigated 

 are destroyed by relatively mild oxidizing agents. In this study it was 

 found that iodine as an oxidizing agent did not destroy the activity of an 

 enzyme completely in any instance. Instead, a progressive inhibition of 

 enzyme activity took place with increasing concentrations of iodine. 



Tincture of iodine contains alcohol which depresses the surface tension 

 of the substrate. Lowering of the surface tension causes an increase in 

 adsorption and, as a result, the enzyme becomes inactive, since a large 

 part of it passes into the foam when milk samples are shaken or rotated. 

 This is the explanation given by Waksman and Davidson (3). It is pos- 

 sible that minute quantities of iodine are non-toxic and actually stimulate 

 enzymic activity in a manner similar to the action of certain drugs on 

 the human body. This may explain the stimulating effect of iodine noted 

 with some of the enzymes. 



In general it can be said that where there was a stimulating effect on 

 enzyme activity, organic iodine was responsible; and where inhibition was 

 noted, the effect was due to inorganic iodine, with the organic having 

 less effect or none at all. 



References 



1. Lane-Claypon, J. E. Milk and its hygienic relation. Medical Re- 

 search Committee. Longmans, Green, and Co., London. 1916. 



2. Cohen, C, and Ruelle, G. Plea in favor of raw milk. Rev. Fran, 

 de Pediatr. 8:312. 1932. 



3. Waksman, S. A., and Davidson, W. C. Enzymes. Williams and 

 Wilkins Co., Baltimore. 1926. 



4. Clifford, W. M. The effect of halogen salts on tryptic digestion. 

 Biochem. Jour. 27:326. 1933. 



5. Steppuhn, O., and Timofejewa, A. Modifying autolysis by iodine. 

 Biochem. Ztschr. 174:84. 1926. 



6. Haldane, J. 1'. S. Enzymes. Longmans, Green, and Co., London. 

 1930. 



7. Gerbcr, G. Influence of halogens upon the action of coagulating and 

 amylolytic enzymes. Compt. Rend. Soc. Biol. 112:112. 1923. 



8. Raudnitz, R. W. Cited from Associates of L. A. Rogers. Funda- 

 mentals of Dairy Science. Rheinhold Pub. Corp., New York. 1935. 



9. Palmer, L. S. Laboratory Experiments in Dairy Chemistry. John 

 Wiley and Sons, Inc., New York. 1926. 



10. Rice, V. F., and Hanzawa, T. Quantitative estimation of peroxidase 

 activity in milk. Jour. Indus, and Fngin. Chem. 14:201. 1922. 



11. Rice, V. K., and Marklcy, A. L. I'roof of the presence of lipase in 

 milk, and a new method for the detection of the enzyme. Jour. Dairy 

 Sci. 5:64. 1922. 



