780 VII. LIPID DISTRIBUTION IN SPECIFIC TISSUES 



scopic analyses revealed the presence of only 1% of 7-dehydrocholesterol. 

 The major component of the fast-reacting sterol fraction which was iso- 

 lated by chromatographic separation of its azoyl ester on silica was shown 

 to be A 7 -cholestene-3/3-ol. 419 



b. Phospholipids in the Skin. The phospholipid level present in the two 

 corium layers does not vary with the triglyceride content of the skin, but 

 remains fairly constant. Koppenhoefer 403 suggests that this indicates that 

 the phospholipids are associated with the fundamental protoplasmic struc- 

 ture, namely the fibroblasts of the corium. 



Much higher amounts of phospholipids occur in the basal layer of the 

 epidermal region. This is also the location in which the nucleated cells 

 present maximum development. In Koppenhoefer's studies, an appre- 

 ciable decline in phospholipids occurred in the horny layer; none could be 

 identified in the lipid isolated from hair. 403 As indicated earlier, the dis- 

 appearance of the phospholipid from this area is believed to reflect a de- 

 struction which occurs during keratinization. The hydroxylated fatty 

 acids present in the wax produced by the sebaceous glands probably orig- 

 inate from the phospholipid fatty acids. 



Both lecithin and cephalin are present in the several skin layers; in 

 general, the lecithin represents the phospholipid present in the higher con- 

 centration. Thus, the proportions of the acetone-insoluble phospholipid 

 precipitated as lecithin and as cephalin, respectively, were found to be as 

 follows 403 : horn division, 41.3 and 6.2%; basal epidermal region, 67.0 and 

 9.9%; transitional region, 7.2 and 18.0%; corium major layer, 68.9 and 

 4.2%; and corium basal layer, 34.5% and not determined. 



The iodine number of the lecithin fraction decreases in the outer layers. 

 Koppenhoefer 403 found the following iodine numbers for the several phos- 

 pholipid fractions: corium major, 83.0; basal epidermal region, 77.2; 

 and horn layer, 66.5. In contradistinction to this progressive decrease in 

 iodine number occurring toward the outer layers of the skin, the acetyl 

 value showed the opposite response (51.2, 52.1, and 74.9, respectively). 

 The cephalin fraction contained fatty acids with a greater degree of un- 

 saturation and higher molecular weights than those present in lecithin. 



c. Waxes in the Skin. Koppenhoefer and Highberger 402 were able to 

 prepare isohydroxystearic acid, stearic acid, and n-eicosanol (arachyl 

 alcohol) from the waxes prepared from steer skin. The last compound has 

 been isolated by Ameseder 420 from a dermoid cyst. The presence of 



419 D. R. Idler and C. A. Baumann, J. Biol. Chem., 195, 623-628 (1952). 



420 F. Ameseder, Z. physiol. Chem., 52, 121-128 (1907). 



