Steryl palmitates

In developing wheat seeds there was little accumulation of sterols up to 14 days after anthesis, but rapid accumulation thereafter (Torres and Garcia-Olmedo, 1975). In one variety where 16 0 SE predominates in the endosperm, the conversion of free sterol to steryl palmitate takes place between 28 days after anthesis and maturity. SG and ASG, which are minor sterolic compounds of wheat endosperm, accumulate steadily from 21 days after anthesis to maturity. 

The overall metabolism of vitamin A in the body is regulated by esterases. Dietary retinyl esters are hydrolyzed enzymatically in the intestinal lumen, and free retinol enters the enterocyte, where it is re-esterified. The resulting esters are then packed into chylomicrons delivered via the lymphatic system to the liver, where they are again hydrolyzed and re-esterified for storage. Prior to mobilization from the liver, the retinyl esters are hydrolyzed, and free retinol is complexed with the retinol-binding protein for secretion from the liver [101]. Different esterases are involved in this sequence. Hydrolysis of dietary retinyl esters in the lumen is catalyzed by pancreatic sterol esterase (steryl-ester acylhydrolase, cholesterol esterase, EC 3.1.1.13) [102], A bile salt independent retinyl-palmitate esterase (EC 3.1.1.21) located in the liver cell plasma hydrolyzes retinyl esters delivered to the liver by chylomicrons. Another neutral retinyl ester hydrolase has been found in the nuclear and cytosolic fractions of liver homogenates. This enzyme is stimulated by bile salts and has properties nearly identical to those observed for... 

The employment of 1,3-selective lipases leads to structured TAG where specific acyl groups are confined to either the l-(3-) or 2-acylglycerol position. One of the earliest examples is cocoa butter substitute formed by 1,3-selective lipase-catalyzed acidolysis (reaction 1 of Fig. 3) of palm oil midfraction by palmitic acid (resulting in the replacement of 1-, 3-dipalmityl, 2-oleyl TAG by l-(3-) palmityl, 2-oleyl, 3- (1-) steryl TAG and 1-, 3-disteryl, 2-oleyl TAG, both of which are abundant in cocoa butter). The product... 

A particular type of wax ester, a steryl ester, is produced where the alcohol unit to which the fatty acid is joined is a sterol.These are also waxy solids, an example being lanosteryl palmitate in lanolin, which is found on sheep s wool. 

Cholesteryl oleate was probably a component of the mixture of steryl esters described in fine-cured tobacco by Rowland and Latimer (3358) and in tobacco smoke by Rodgman et al. (3296). The steryl esters included sterols esterified with a series of saturated (palmitic, stearic, etc) and unsaturated (oleic, linoleic, etc.) acids. 

Esterified by a fatty acid (steryl esters), e.g., sitosteryl palmitate (Sticher 2007 and references therein)... 

---