Bilirubin solubilization

Once bilirubin enters the hepatocytes, it can bind to certain cytosolic proteins, which help to keep it solubilized prior to conjugation. Ligandin (a family of glutathione S-transferases) and protein Y are the involved proteins. They may also help to prevent efflux of bilirubin back into the blood stream. 

Only results obtained with albumin-solubilized bilirubin are given human serum (HS), rat serum (RS), albumin (A), human serum albumin (HA), bovine serum albumin (BA). Figures between parentheses indicate the molecular ratio, bilirubin albumin. 

It may be difficult to conserve initial velocities over a sufficient period of time to warrant appropriate sensitivity of the assays, especially with unactivated enzyme preparations. With carrier-free bilindiin substrate, decrease of the initial velocity may occur earlier than with albumin-solubilized bilirubin ( 116). Spontaneous activation (W7) of enzyme... 

Some authors have used carrier-free enzymatic incubation mixtures at pH 8.0-8.3 (J5, P3, W12). In general, the final concentrations used (incubation at 37°C) were 5-10-fold higher than the solubility of bilirubin at 25°C (B25). Although solubility data at 37°C are not available, it is likely that in most instances the solubility was exceeded. It is not known whether, and to what extent, bilirubin is solubilized in an aspecific way, e.g., by dissolution in lipid membrane regions. Formation of colloidal bilirubin is possible (B25). Aging of the initial, supersaturated (B25) bilirubinate solution is expected to depend (B26) on the procedure of initial solubilization, the time elapsed between lowering the alkaline... 

With albumin-solubilized bilirubin, pH optima of microsomal bilirubin UDP-glucuronyltransferase were 7.4-8.0 for rat (H2, HIO, SIO) and 7.4 for guinea pig (M13) and rabbit (T8). Above pH 8 the enzyme activity decreased abruptly (HIO). In absence of carrier protein, optima were at pH 8 and 8.2 with preparations from liver of guinea pig (P3) and rat (W12), respectively. The activity-pH curve with optimum at pH 8.2 (W12) showed pronounced skewing, with a steady and rather rapid increase of enzyme activity from pH 7.4 to 8.2. One may wonder whether such measurements were influenced by the rapid increase of solubility of the acceptor substrate occurring over the same pH range (B25). 

Bilirubin is a lipid-soluble substance and for it to give a direct van den Bergh reaction it must be converted into a water-soluble state. This can be achieved in alkaline solution or by the use of solvents, such as ethanol, which are soluble in both water and chloroform (Cl). Conjugation with glucuronic acid also causes the solubilization of bilirubin and in view of the well-known versatility of the liver s detoxifying systems, the possibility that bilirubin may be conjugated with other substances has been considered. 

The complexation of bilirubin by 6-cyclodextrin leads to the observation of remarkably intense induced CD, which has been attributed to the preferential stabilization of chiral molecular conformations [63]. In addition, the bilirubin solute may be sufficiently solubilized in alternate solvents so that new analytical methods can be developed for its determination. This latter feature of the complexation phenomenon is of analytical significance, since quantitation... 

Bile fluid performs two important functions (1) the emulsification, solubilization, and transport of lipids and fat-soluble vitamins by the detergent effects of bile acids, and (2) the elimination of many waste products, including bilirubin and cholesterol secreted via the bile into the gastrointestinal tract. Bile acids and bile salts are the principal components of the bile fluid, acting as detergents in the digestion of fat in the intestinal tract. 

Halac and Refi found that liver fractions from rats are capable of conjugating bilirubin and p-nitrophenol with D-glucuronic acid. The D-giucosyluronic transferase has been solubilized by treating EDTA-activated microsomes with deoxycholate. The results were compatible with the existence of a UDP-D-glucosyluronic transferase for bilirubin that differs from the enzyme that catalyzes the formation of p-nitrophenyl /8-D-glucosiduronic acid. 

Uses Lipase accelerator solubilizer for unconjugated bilirubin anionic detergent for protein solubilization... 

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