202 Microscopic Histochemistry 



The substrate specificity of even the two large groups (aU- 

 esterases and cholinesterases ) is not an absolute one; actu- 

 ally, both types will attack choline and noncholine esters. ^^^""^ 

 The sharpest difference between any two groups of the sys- 

 tem is in the sensitivity of esterases toward eserine and simi- 

 lar alkaloids. Chohnesterases are inhibited by concentrations 

 of 10~^ M or less/^*' -^^^ while aliesterases are insensitive to as 

 much as 10"^ M.^^^ It is impossible to go into the details of 

 the highly complex problem of the specificity of esterases; it 

 is suggested that the interested reader study the original 

 articles referred to. 



I. ALIESTERASES 



A suitable histochemical substrate for esterases must sat- 

 isfy the following three conditions: (1) It must be suffi- 

 ciently soluble in water, because esterases do not work in 

 nonaqueous media. Kurata and Hoso^^^ did get positive re- 

 sults with a suspension of olive oil; however, the method is 

 very insensitive, showing only sites of extremely high activ- 

 ity. (2) It must by hydrolyzable by enzymes. (3) One of 

 the split products must be precipitable in statu nascendi. Up 

 to 1945 it appeared as if the three conditions were mutually 

 exclusive. The first substrates to be used histochemically^^^ 

 were the Tweens, which are long-chained (C12-C18) fatty 

 acid esters of sorbitan or mannitan, the remaining hydroxyl 

 groups of which are etherified with ethylene oxide chains of 

 varying lengths. These substances are water-soluble, readily 

 attacked by esterases, and the fatty acid liberated can be 

 trapped in the form of insoluble Ca soaps. Esters of poly- 



105. Stedman, E., Stedman, E., and V^hite, A. C: Biochem. J., 27:1055, 

 1933. 



106. Easson, L. H., and Stedman, E.: Biochem. J., 31:1723, 1937. 



107. Mendel, B., and Rudney, H.: Biochem. J., 37:59, 1943; Holton, P.: 

 Biochem. J., 43:13, 1948; Zeller, E. A.: Helvet. physiol. et pharmacol. acta, 

 6:C36, 1948; Whittaker, V. P.: Biochem. J., 44:46, 1949; McNaughton, 

 R. A., and Zeller, E. A.: Proc. Soc. Exper. Biol. & Med., 70:165, 1949. 



108. Huggins, C, and Moulton, S. H.: J. Exper. Med., 88:169, 1948. 



109. Kurata, Y., and Hoso, M.: Igaku to Seibutzugaku, 18:103, 1951. 



110. Gomori, G.: Proc. Soc. Exper. Biol. & Med., 58:362, 1945. 



