Enzymes 203 



ethylene glycols, marketed under various trade-names, have 

 essentially similar properties. 



The other type of substrate are esters of naphthols^^^ ( ace- 

 tates or benzoates ) . The naphthol liberated is demonstrated 

 by azo-coupling. 



The best fixation for esterases and lipases is, acetone, but 

 alcohol is almost equally good. Relatively short (12-24 

 hours) fixation in 10 per cent formalin (preferably neutral- 

 ized and at icebox temperature) is permissible, although, 

 compared with acetone-fixed tissues, 50-75 per cent of the 

 enzyme will be destroyed by it. 



A. The Tween technique.— 



Most of the lauric, palmitic, stearic, oleic, ricinoleic, or 

 mixed esters available on the market are usable, provided 

 that they are soluble in water. The rate of hydrolysis drops 

 with increasing chain length, laurates being the fastest and 

 stearates the slowest substrates. However, the crystal size of 

 the precipitate also decreases with increasing chaia length, 

 and localization is far more accurate with the slow stearates 

 than with the faster laurates, which produce rather coarse 

 crystals. ^^^ The following substrates are recommended for 

 use: 



Saturated subtrates: 



1. Stearates 



Tween 60 (Atlas Powder Co., Wilmington, Del.) 



G-9096-CJ (Atlas) 



G-2151 (Atlas) 



Product No. 81 (Onyx Oil and Chemical Co., Jersey City, N.J.) 



2. Palmitate 

 Tween 40 (Atlas) 



3. Laurate 



Tween 20 (Atlas) 



111. Nachlas, M. M., and Seligman, A. M.: J. Nat. Cancer Inst., 9:415, 

 1949; Nachlas, M. M., and Seligman, A. M.: Anat. Rec, 105:677, 1949. 



112. Gomori, G.: Methods of study for tissue Hpase. In Menstruation and 

 its disorders (Springfield, 111.: C. C. Thomas, 1950). 



