176 Microscopic Histochemistry 



single enzyme or a group of enzymes with closely similar, 

 although not identical, properties has been a matter of con- 

 siderable argument. There is a large body of chemical data 

 available in support of the theory of plurality.^ Alkaline phos- 

 phatases of different sources may show marked difiFerences 

 in substrate preference and in their susceptibility to various 

 activators and inhibitors. However, even if all the enzymes 

 reported to exist do actually represent truly individual en- 

 tities, the majority of them appear to be destroyed in the 

 course of fixation and/or embedding. There are a consider- 

 able number of reports asserting that the localization of ac- 

 tivity depends on the substrate used and that the differences 

 observed are due to the presence of several enzymes;^^^** ^'^ 

 however, since the results have been obtained mostly under 

 highly unfavorable conditions (prolonged incubation at low 

 pH levels ) , the evidence cannot be accepted at face value. 

 The slight variations due to different substrates may very 

 well be considered the expression of differences in the rates 

 of hydrolysis and in optimal pH values, the enzyme being 

 identical in all cases ( see p. 172 ) . The writer found that un- 

 der optimal or near-optimal conditions the pictures obtained 

 with a large variety of substrates were indistinguishable from 

 one another. Moog,^^ Ross and Ely,^* Zorzoli and Stowell,^^ 

 and other s^^ have come to a similar conclusion. The only 

 exception is 5-nucleotide : this substance is hydrolyzed by a 

 specific enzyme. It should be emphasized specifically that 



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 1946; Dempsey, E. W., and Singer, M.: Endocrinology, 38:270, 1946; 

 Deane, H. W.: Am. J. Anat, 80:321, 1947; Dempsey, E. W., and Wislocld, 

 G. B.: Am. J. Anat., 80:1, 1947; Siillmann, H.: Ztschr. f. Vitamin-, Hormon- 

 u. Fermentforsch., 1:374, 1947-48; Lagerstedt, S., and Stenram, U.: Acta 

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 Am. J. Path., 26:257, 1950. 



19. Moog, F.: Biol. Bull., 86:51, 1944. 



20. Zorzoli, A., and Stowell, R. E.: Anat. Rec, 97:495, 1947. 



21. Bevelander, G., and Johnson, P. L.: Anat. Rec, 104:125, 1949; 

 Hebert, S.: Arch, de biol., 61:235, 1950. 



