CHANGES IN THE INTESTINAL WALL 453 



horse liver. Yudkin^*^ made the converse observation, i.e., that the retinal 

 enzyme of the frog oxidizes ethyl alcohol to acetaldehyde. Wald^'* is now 

 also of the ophiion that alcohol dehydrogenase and retinene reductase are 

 identical; he suggests that retinene reductase should be referred to by the 

 more general designation. The same enzyme functions with both the 

 rhodopsin and the porphyropsin system, in one case reducing retinenei 

 to vitamin Ai and in the second instance changing retinene2 to vitamin Ao. 

 Wald-^^'^** showed that both systems are interchangeable and that both 

 have the same coenzyme. 



Two alcohol dehydrogenase systems are known, both of which catalyze 

 the equilibrium between ethyl alcohol and acetaldehyde. One of the dehy- 

 drogenase systems is present in animal tissues, while the second occurs in 

 yeast. Bonnichsen^*® crystallized the first type from horse liver, while 

 Xegelehi and Wulff-" and Racker'^"^ prepared the second variety in crys- 

 talline form from yeast. According to Bonnichsen"^ and Bliss,^**' the 

 yeast enzj^me is inactive in catalyzing the retinene -*- vitamin A reaction. 

 For a further discussion of the nature of these enzj^me systems, the reader 

 is referred to the article by Wald, in Sebrell and Harris, The Vitamins, 

 Vol. I.25» 



b. The Role of Alcohol Dehydrogenase in Carotene Utilization. The 

 alcohol dehydrogenase sj^stem in the gut wall is believed to play a part in 

 the conversion of carotene to vitamin A. Glover and co-workers^*^ sug- 

 gested that vitamin A aldehyde is an intermediate in the carotene — »- vi- 

 tamin A reaction. 



The formation of \dtamin A aldehyde has been repeatedly demonstrated 

 in the in vitro oxidation of iS-carotene. Thus, Hunter and Williams^^^ 

 noted that small amounts (0.4 to 0.5%) of this aldehj^de were formed when 

 /3-carotene was oxidized with hydrogen peroxide in a glacial acetic acid 

 solvent. A yield of as much as 30% of "vitamin A aldehyde was obtained 



'''^ W. Yudkin, Unpublished experiments; cited by G. Wald, Biochemical Systems, 

 ill W. H. Sebrell, Jr., and R. S. Harris, The Vitamins, Vol. I, Academic Press, New York, 

 1954, p. 67. 



^^^ G. Wald, Biochemical Systerris, in W. H. Sebrell, Jr., and R. S. Harris, The Vita- 

 mins, Vol. I, Academic Press, New York, 1954, pp. 59-87. 



"* G. Wald, Science, 109, 482-483 (1949). 



235 G. Wald, Biochim. et Biophijs. Acta, 4, 215-228 (1950). 



23« R. K. Bonnichsen, Acta Chetn. Scand., 4, 715-716 (1950). 



2" E. Negelein and H. J. WulGF, Biochem. Z., 293, 351-389 (1937). 



238 E. Racker, J. Biol. Chem., 184, 313-319 (1950). 



239 R. K. Bonnichsen, personal communication; cited bv R. Hubbard and G. Wald, 

 Proc. Xat. Acad. Sci., U.S., 37, 69-79 (1951), p. 75. 



2« A. F. Bliss, Arch. Biochem. Biophys., 31, 197-204 (1951). 



2" R. F Hunter and N. E. Williams, J. Chem. Soc, 1945, 554-556. 



