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EC number: 701-023-5
CAS number: 85408-61-3
Enzymatic Lipolysis by Gastric and Duodenal Juice:
All samples of gastric juice showed lipolytic activity against
trioctanoin and triolein. Hydrolysis of emulsified trioctanoin was
greater than of emulsified triolein. Hydrolysis of unemulsified
trioctanoin was less and more variable.
Duodenal juice was more active, even against unemulsified trioctanoin
and triolein. Duodenal juice was more active against unemulsified
substrate than gastric juice against emulsified substrate.
Table 1: Hydrolysis of trioctanoin and triolein*
Substrate and form
*Gastric or duodenal juice (1 mL) was incubated (1 hour, continuous
shaking, 37ºC) with 1 mL of buffer and unemulsified substrate or 1 mL of
substrate emulsified in 10 mM sodium taurodeoxycholate, pH6.
In the presence of bile acids, gastric lipolytic activity against
trioctanoin had a broad pH optimum, between 4 and 7. The lipolytic
activity of duodenal juice had a sharper pH optimum, between 6 and 8.
The pH optimum was lower for short chain triglycerides, indicating that
pH optimum values for lipases must be defined for a particular substrate.
Chain Length Specificity
Lipolysis rates increased with decreasing chain lengths for pure
Tributyrin was cleaved more rapidly than trihexanoin which in turn was
cleaved more rapidly than trioctanoin (ratio of rates, 100:69:53).
Because the pH optimum of gastric lipase is lower for short chain
triglycerides than for MCT, trihexanoin and tributyrin were cleaved much
more rapidly than, for example, trioctanoin at pH5.
Esterification and Fatty Acid Acceptors by Gastric and Duodenal
Gastric and duodenal lipases did not induce esterification of the fatty
acid acceptor, glyceryl 2 -monooleyl ester, by octanoic acid over the pH
range of 2 to 6. However, it was esterified by oleic acid in the
presence of gastric juice, duodenal juice, or pancreatic fistula juice
when bile acids were added. Esterification, calculated by disappearance
of titratable fatty acid, was confirmed by TLC which showed the
formation of compounds having the mobilities of a monoether monoester
and a monoether diester. Control incubations without enzyme showed no
loss of oleic acid or appearance of new lipids by TLC. To determine the
amount of disubstituted and trisubstituted glyceryl derivatives which
were formed, 14C-labeled glyceryl 2 -monooleyl ether was used and the
products of the reaction were examined by zonal scanning. The glyceryl 2
-monooleyl ether was not cleaved during the incubation procedure. The
amounts of ester bonds formed estimated by titration and by zonal
scanning were in good agreement.
Products of Lipolysis and Positional Specificity
The specificity of pancreatic lipase for the 1 -ester bond in LCT has
been demonstrated previously by establishing the formation of 2
-monoglycerides and fatty acid as end products of lipolysis. This
procedure cannot be used for MCT because medium chain 2 -monoglycerides
are either cleaved by pancreatic lipase or rapidly isomerized to the 1
-isomer which is rapidly hydrolyzed or both. Indeed, chromatographic
examination of the products of hydrolysis of trioctanoin-14C showed only
a small fraction of monoglyceride present.
Table 2: Products of hydrolysis of trioctanoin by gastric juice*
Radioactivity distribution** (%)
*Glyceryl trioctanoate-1-14C was added to 1 mL of emulsified
trioctanoin (60 μmoles) and incubated for 1 hour at 37ºC with buffer
(blank) or gastric or duodenal juice. The reaction mixture was extracted
and a 50 μL aliquot was analyzed by TLC and zonal scanning. A 3 mL
aliquot was titrated to quantify fatty acids liberated.
The work confirmed extensive literature showing that gastric juice
contains lipolytic activity, that ingested triglyceride is hydrolyzed in
the stomach, even after pancreatic diversion, that lipase may be
demonstrated histochemically in gastric mucosa, and that gastric mucosal
homogenates have lipolytic activity. Pancreatic lipase has some activity
at the pH of gastric content, which is between pH6 and pH3 in normal
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