DIGESTION, ABSORPTION, AND DIGESTIBILITY 433 



sary preliminary change occurring in the intestine prior to absorption.^' 

 Gray et al.^^ are of the opinion that an esterase in the intestinal juice is 

 responsible for this, hydrolysis. Ganguly^^ reported the presence of an 

 enzyme in pig pancreas capable of hydrolyzing vitamin A esters. A vita- 

 min A esterase in rat liver homogenates was also described by McGugan 

 and Laughland.^^ This observation was confirmed by Ganguly and 

 Deuel, ^^ who made the further discovery that the enzyme occurs in the 

 microsomal fraction of the homogenate, while the nuclear, mitochondrial, 

 and supernatant fractions contain no enzyme. On the other hand, Krause 

 and PowelP^ reported that the activity of the liver in hydrolyzing vitamin A 

 acetate was not concentrated in any particular fraction, but that it was 

 distributed throughout the various fractions of rat liver homogenate. 

 Homogenates of intestine and kidney are able to esterify vitamin A. 

 Liver homogenates and their cellular components are unable to carry out 

 this reaction. In an extension of his studies, Ganguly®^ again demonstrated 

 quantitatively the presence of the esterase in the microsomal fraction of 

 rat liver homogenates, and its absence in the other fractions. The pan- 

 creatic esterase is largely concerned with the hydrolysis of the vitamin A 

 esters in the lumen of the gut.^^ 



A number of experiments support the theory that an intestinal hydrolysis 

 of vitamin A esters takes place. Not only does a gradual increase in 

 vitamin A alcohol occur in the intestinal contents as digestion proceeds, 

 after vitamin A ester is given to rats, but a concomitant increase in vitamin 

 A, largely in the form of the free alcohol, occurs in the intestinal wall.^' 

 Eden and Sellers^'' confirmed the occurrence of this hydrolysis in the case 

 of calves and sheep, and the data of Clausen^^ and of Popper and Volk^^ 

 offer further support for this hypothesis. Lovern and co-workers ^™'^°^ 

 suggest that, in the ease of the fishes, the vitamin A alcohol may mediate 

 the absorption of the fatty acids by a mechanism involving repeated esteri- 



" E. L. Gray, K. Morgareidge, and J. D. Cawley, /. Nutrition, 20, 67-74 (1940). 



82 J. Ganguly, Thesis, Univ. Reading (Gt. Britain), 1949; cited by J. Ganguly and 

 H. J. Deuel, Jr.^ Nature, 172, 120-121 (1933), p. 120. 



83 W. A. McGugan and D. H. Laughland, Arch. Biochem. Biophys., 35, 428-434 

 (1952). 



9^ J. Ganguly and H. J. Deuel, Jr., Nature, 172, 120-121 (1953). 



95 R. F. Krause and L. T. Powell, Arch. Biochem. Biophys., U, 57-62 (1953). 



9« J. Ganguly, Arch. Biochem. Biophys., 52, 186-189 (1954). 



" E. Eden and K. C. Sellers, Biochem. J., 45, x.x.xiii (1945); 46, 261-266 (1950). 



98 S. W. Clausen, Harvey Lectures, 38, 199-226 (1943). 



99 H. Popper and B. W. Volk, Arch. Pathol., 38, 71-75 (1944). 



100 J. A. Lovern and R. A. Morton, Biochem. J., 33, 330-337 (1939). 



101 J. A. Lovern, T. H. Mead, and R. A. Morton, Biochem. J., 33, 338-343 (1939). 



