274 IV. DIGESTION OF LIPIDS OTHER THAN PATS 



coprostanol was formed. 142 However, when the basal diet consisted of 

 dog biscuits, cholesterol was found to be the excretion product of chole- 

 stenone. 142 In a later report, Anchel and Schoenheimer 146 demonstrated 

 the conversion of deuteriocholestenone to deuteriocoprostanol in man. 

 After deuteriocholestenone was fed to mice, the cholesterol contained no 

 appreciable amount of deuterium; this may mean that cholestenone 

 cannot be converted to cholesterol in mice, as is possible in the dog, or 

 that the labile deuterium is lost during the reaction. 



Proof that coprostanone is likewise an intermediate in the biological 

 transformation of cholesterol to coprostanol has been obtained by the 

 use of tagged molecules. Thus, when deuteriocoprostanone was fed to 

 dogs 142 or to man, 146 the administration was followed by the excretion of 

 deuteriocoprostanol in the feces. Another proof of the hypothesis that 

 3-ketone compounds are intermediates in the conversion of cholesterol to 

 coprostanol is the fact that both epicoprostanol and coprostanol occur in 

 the feces. 151 



Another change, analogous to the cholesterol -*■ coprostanol reaction, 

 is the conversion of /3-sitosterol to 24-ethylcoprostanol. 119 Turfitt 152-154 

 demonstrated that a soil bacterium, Proactinomyces spp., especially P. 

 erythropolis, oxidizes cholesterol to cholestenone; following this, the side 

 chain is partially ruptured, resulting in the production of A 4 - 5 -3-keto- 

 etiocholanic acid, and Ring A is split between C 3 and C4 to yield a keto- 

 carboxylic acid. 155 There is no indication that intestinal bacteria can 

 bring about a similar degradation of cholesterol. 



(5) The Transport of Cholesterol from the Gut 



As early as 1916, Mueller 63 - 64 demonstrated that cholesterol is readily 

 absorbed from the intestine of the dog, and that it passes into the lym- 

 phatics, where it can be detected in the thoracic duct lymph. It was 

 found that the proportion of cholesterol esterified in the lymph is the 

 same, irrespective of whether the cholesterol is given in free or in ester 

 form. Biggs, Friedman, and Byers 156 reported that exogenous cholesterol 

 is conveyed into the systemic circulation via the lymphatics into the 



161 R. E. Marker, E. L. Wittbecker, R. B. Wagner, and D. L. Turner, ./. Am. Chem. 

 Soc., 64, 818-822 (1942). 



162 G. E. Turfitt, Biochem, J., 38, 492-496 (1944). 



163 G. E. Turfitt, /. Bacterid., 47, 487-493 (1944). 



164 G. E. Turfitt, Biochem. J., 40, 79-81 (1946). 

 158 G. E. Turfitt, Biochem. J., 42, 376-383 (1948). 



188 M. W. Biggs, M. Friedman, and S. O. Byers, Proc. Soc. Exptl. Biol. Med., 78, 641- 

 643 (1951). 



