In this study, a covalent bilirubin-binding amino acid residue of the albumin molecule in δ bilirubin was identified. Icteric human serum was treated with a diazo reagent and bilirubin was converted ...to a stable azodipyrrole. Then, an albumin fraction containing an azodipryrrole-albumin covalent conjugate was obtained by affinity chromatography using Blue Sepharose CL-6B, and it was further purified by reverse phase high performance liquid chromatography. To identify the covalently bound azodipyrrole amino acid residue in albumin, the azodipyrrole-albumin conjugate was cleaved to fragmented peptides by chemical and enzymatical methods, and three main peptide fractions which had the absorption characteristics of azodipyrrole at 530 nm were isolated. Their amino acid sequence analysis revealed that all of the peptides corresponded to residues 187–191 in albumin, where lysine residue 190 was identified as the covalent-binding site of albumin to bilirubin in δ bilirubin.
Crigler-Najjar syndrome (types I and II) and Gilbert's syndrome are familial disorders associated with severe to mild unconjugated hyperbilirubinemia. In these conditions, the activity of bilirubin ...UDP-glucuronosyltransferase (UGT1
∗1), which is located in the hepatocyte endoplasmic reticulum, is defective, and severely and moderately decreased, respectively. UGT1
∗1 is derived from one of the UGT1 genes. It has a promoter containing a TATA box and consists of exon 1A (which is one of the individual first exons) and common exons 2–5. UGT1
∗1 mRNA is formed by differential splicing of these exons. In recent years, gene analysis of these syndromes has been carried out, and genetic abnormalities have been clarified. Homozygous nonsense mutations, mis-sense mutations, and other relevant mutations of exons 1A-5 have been reported in almost all of the patients with Crigler-Najjar syndrome type I, while mainly homozygous mis-sense mutations of exons 1A, 2, and 5 have been reported in type II patients. Almost all patients with this syndrome (types I and II) show autosomal recessive inheritance. On the other hand, some patients with Gilbert's syndrome show heterozygous mis-sense mutations in exons 1A, 4, and 5, while others show homozygous 2-base pair-insertion mutation (TA) into the TATA box in the promoter region A(TA)
7TAA; normal: A(TA)
6TAA. The pattern of inheritance can be autosomal recessive or autosomal dominant. It has also been clarified that enzyme activity is lowered to about 30% (rather than 50%) by heterozygous mutations of the coding region, because of the occurrence of dominant negative mutation based on subunit-structure of the enzyme.
To elucidate the possible implication of hepatic blood supply to the occurrence of hepatolithiasis, the rat superior mesenteric vein, which drains blood from the intestine, or the splenic vein, which ...drains from the spleen, was occluded for 30 minutes. Changes in the hepatic oxygen saturation index, intrahepatic uridine diphosphate-glucuronic acid concentration, bile flow, and the excretion of bilirubin as well as its fraction, along with bile acid in bile before and after the procedure, were observed. In association with superior mesenteric vein occlusion, oxygen saturation index, hepatic uridine diphosphate-glucuronic acid concentration, bile flow, bile acid concentration in bile, and percentage of biliary bilirubin diglucuronide were all decreased. Incubation of bile under sterile conditions from rats with occluded superior mesenteric veins resulted in precipitation of mainly calcium salt of fatty acid. In contrast, splenic vein occlusion caused no changes except for a decrease in biliary bilirubin concentration. Incubation of bile from rats with occluded splenic veins did not induce precipitation. From these findings it can be concluded that blood flow in the superior mesenteric vein is the primary source of oxygen supply to the rat liver and that this vein plays an important role in maintaining bile flow, bile acid excretion, and bilirubin conjugation and in preventing the precipitation of bile (possibly preventing hepatolithiasis).
Transport of various intrinsic and extrinsic organic anions across the canalicular membrane of hepatocytes has been confirmed to occur via ATP-dependent primary active transport. To investigate these ...processes in the presence of obstructive jaundice, the uptake of radiolabeled taurocholate and pravastatin, a non-bile acid organic anion, by isolated hepatocyte canalicular membrane vesicles was observed after bile duct ligation in rats. The Mg
+ +-ATPase and Na
+, K
+ -ATPase activity did not differ between membrane vesicle preparations from sham-operated and bile duct-ligated rats. Taurocholate uptake decreased significantly to 45% and 29%, while pravastatin uptake decreased to 35% and 35% of that in sham-operated rats at 2 and 7 days after bile duct ligation. These results indicate that the ATP-dependent transport systems for both bile salts and non-bile acid organic anions are impaired soon after the onset of obstructive jaundice.
