Search

1. Interaction of bilirubin with collagen fibrils was explored in a two-phase system where collagen was present as an opaque rigid gel composed of striated fibrils, and bilirubin as an aqueous solution. 2. The Ka value of the binding of bilirubin to collagen fibrils is 5.4 X 10(3)M-1. The interaction of bilirubin with collagen fibrils depends on temperature. Below 5 degrees C, the binding is greatly diminished and denaturation of collagen fibril aggregates at 52--53 degrees C into a dissolution state abolishes binding of bilirubin. 3. Salicylate and sulphanilamide do not affect the binding of bilirubin to reconstituted collagen fibrils. 4. Serum albumin (40--80mM), known to reverse the binding of bilirubin to lipids, dissociates only 50% of the bilirubin bound to collagen fibrils. This suggests that sites located on collagen participate in some tight binding of bilirubin and the corresponding binding sites on albumin do not compete with them. 5. Urea (4M) abolishes more than 70% of the binding of bilirubin to collagen. Urea and thermal denaturation studies indicate the importance of conformation and organization of collagen fibrillar aggregates for the binding of bilirubin.

1. Human skin epithelium and human skin were found to absorb both free bilirubin and serum-bound bilirubin from an aqueous buffered medium. The serum-bound bilirubin thus absorbed was readily released when human skin epithelium or human skin were transferred to media containing no bilirubin. 2. The K(m) values for serum-bound bilirubin were 1.8x10(-3)m and 2.2x10(-3)m respectively for human skin epithelium and human skin; corresponding K(m) values for free bilirubin were 3.0x10(-4)m and 5x10(-4)m. The V(max.) for bound and free bilirubin was of the same magnitude, the apparent V(max.) being 1.0 and 1.66mumol/g of tissue for human skin epithelium and human skin respectively. 3. When human skin that had acquired a yellow tinge by absorbing bilirubin was incubated in a buffered medium and exposed to a mercury-vapour light, the yellow colour disappeared and decomposition products of bilirubin accumulated in the medium. 4. Experiments with [(3)H]bilirubin indicated that the pigment absorbed by skin was photo-oxidized to products that were soluble in water and the quantity and number of such products increased with the time of exposure of human skin to the light-source. Under similar conditions [(3)H]bilirubin alone in buffered medium was also oxidized and gave products which by paper chromatography appeared to be different from those released by human skin that had absorbed bilirubin. 5. The results suggest that by virtue of its large surface area human skin can act as a matrix for the degradative action of light on bilirubin.

1. Skin epithelium of albino rat, mouse and guinea pig was shown to accumulate bilirubin from a medium containing free or bound bilirubin. 2. The K(m) values for bound bilirubin were 2.22x10(-3), 1.33x10(-3) and 9.5x10(-4)m for rat, mouse and guinea pig respectively and the corresponding K(m) values for free bilirubin were 5.2x10(-4), 4.0x10(-4), 1.8x10(-4)m; the V(max.) values of bound and free bilirubin were unchanged. 3. The uptake showed saturation kinetics. Bound bilirubin was released together with serum proteins. Free bilirubin bound to skin was not released into the medium. 4. Freezing and thawing of skin epithelium did not cause any significant lowering of the uptake of bilirubin but heat-denatured skin epidermis took up only 50% of the bound bilirubin or free bilirubin taken up by control unheated skin epithelium. 5. The uptake of free and bound bilirubin was prevented by HgCl(2) but not by sodium arsenate, NaCN, NaF, cycloheximide, 2,4-dinitrophenol or iodoacetate. 6. Most of the free bilirubin was bound to the lipids or lipoprotein fraction of skin epithelium and could be extracted by solvents. 7. Rat skin showed the highest accumulation and efflux of bilirubin.