204 Microscopic Histochemistry 



Unsaturated substrates: 



1. Oleates 



Tween 80 (Atlas) 

 G-2144 (Atlas) 

 G-9446-N (Atlas) 

 G-7627-DJ (Atlas) 

 Neutronyx R (Onyx) 



2. Ricinoleates (these are especially slow substrates) 

 G-6486 (Atlas) 



Antarox B 290 (General Aniline and Film Corp.) 



3. Mixed linseed oil esters 

 G-9926-T (Atlas) 



The saturated compounds are general substrates for lipase- 

 esterase; they are hydrolyzed by the enzymes of many or- 

 gans. The unsaturated substrates are attacked only by the 

 enzymes of the pancreas and of the chief cells of the mouse 

 stomach^^^ ( "true lipase" ) and are left practically untouched 

 by those of other tissues. Whether the faint reactions ob- 

 tained with these substrates in the intestine, liver, kidney, 

 etc., are due to a slight activity of the enzyme toward the 

 unsaturated ester or to the invariable presence of saturated 

 esters (as impurities) in the commercial unsaturated com- 

 pounds cannot be decided, because purified Tweens contain- 

 ing exclusively unsaturated fatty acids are not available. 



The quality of the Tweens and similar substances varies 

 considerably from batch to batch. Some batches are pure 

 enough to be used directly, others will develop turbidity in 

 the presence of Ca salts, thus indicating the presence of free 

 fatty acid. It is advisable to purify them for histochemical 

 use. The following routine is recommended: 



Dissolve about 5 per cent of Tween in a 0.1 M tris (hydroxy- 

 methyl)-aminomethane or tris-maleate buffer of pH 7-7.4, 

 add about 0.5 per cent of CaCl2 and a few crystals of cam- 

 phor (important: Tweens are excellent nutrient media for 

 many microorganisms!). Incubate at 37° C. for 24-48 hours; 

 filter through a fritted glass plate or a Seitz asbestos filter. 



113. Gomori, G.: Proc. Soc. Exper. Biol. & Med., 72:697, 1949. 



