16 II. DIGESTION AND ABSORPTION OF FATS 



less than that of plasma. However, Brauer and Hardenbergh 93 found that 

 liver lymph contains about 90% of the esterase activity of plasma and an 

 identical proportion of esterase to protein, irrespective of whether the 

 plasma esterase has been elevated by treatment of the animals with carbon 

 tetrachloride, or reduced by the injection of concentrated albumin solutions. 

 These results indicate that the lymph esterase originates from the plasma 

 esterase. This hypothesis is supported further by the finding that the 

 level of plasma tributyrinase is markedly reduced when the lymph is 

 drained externally. 92 



The lymph esterases vary somewhat with the site from which they are 

 obtained. Thus, based upon protein content, cervical lymph has only 

 49% of the activity of plasma. Thoracic and mesenteric lymph esterases 

 show a composition intermediate between that of cervical and that of liver 

 esterase. Finally, liver lymph has been shown to possess 90% of the activ- 

 ity of plasma. 93 The esterase from plasma thus passes into the lymph less 

 readily than do other globulin components of the plasma. 



c. Properties of Esterases. The optimum pH of liver esterases varies 

 between 6.7 and 8.2, depending upon the buffer, the method of preparation, 

 and the source of the enzyme. 94 Esterases of different origin present varia- 

 tions in activity according to the substrate used. In earlier studies, 

 ethyl acetate and ethyl butyrate were usually employed, 95 ' 96 and such dif- 

 ferences in behavior were not noted; when more complex esters were used, 

 many variations in activity could be demonstrated. Thus, while kidney 

 esterase acted 50 to 100% more rapidly on ethyl than on methyl esters, 

 lung esterase hydrolyzed both types equally well. 83 In spite of the fact 

 that liver esterase hydrolyzed ethyl and methyl benzoate at an identical 

 rate, the more rapid splitting of ethyl acetate as compared with methyl 

 acetate was noted. 



Esterases also yield markedly different results when diesters of the di- 

 carboxylic acids serve as substrates. When diethyl malonate (C 3 ) and 

 diethyl succinate (C 4 ) were treated with hog liver esterase, hydrolysis 

 proceeded rapidly, and equilibrium was reached when one ester group per 

 molecule had been removed. 97,98 On the other hand, when the substrate 

 was diethyl glutarate (C 5 ) or diethyl adipate (C 6 ), both ester groups were 

 removed by the time that equilibrium was reached. 



93 R. W. Brauer and E. Hardenbergh, Am. J. Physiol, 150, 746-753 (1947). 



94 H. Sobotka and D. Glick, J. Biol. Chem., 105, 221-230 (1934). 



96 J. H. Kastle and A. S. Loevenhart, Am. Chem. J., 24, 491-525 (1900). 



96 J. H. Kastle, M. E. Johnston, and E. Elvove, Am. Chem. J., 31, 521-550 (1904). 



97 E. C. Hyde and H. B. Lewis, /. Biol. Chem., 56, 7-15 (1923). 



98 D. A. McGinty and H. B. Lewis, J. Biol. Chem., 67, 567-577 ( 1926). 



