No abstract

An ATP/ubiquitin-dependent proteasome complex with an apparent sedimentation coefficient of 26S was purified from rat liver to near homogeneity by an improved method based on procedures reported previously. Two electrophoretically distinct forms of the 26S complex, named 26S alpha and 26S beta, with very similar subunit compositions were found not only in purified preparations but also in crude extracts, indicating that the 26S proteasome is present as two isoforms. The 26S proteasome was shown to degrade multi-ubiquitinated, but not unmodified, lysozymes in an ATP-dependent fashion, to have ATPase activity supplying energy for proteolysis, and to contain isopeptidase activity to generate free ubiquitin Mg2+/ATP-dependently. The 26S proteasome also catalyzed the ATP-independent hydrolyses of three types of fluorogenic peptides with basic, neutral, and acidic amino acids at their cleavage sites, respectively. These peptides are also good substrates for the 20S proteasome, but their degradation by the free 20S proteasome and by its assembled form in the 26S complex differ markedly, suggesting a functional difference between the two forms of proteasomes. Electrophoretic and immunochemical analyses showed that the large 26S complex was composed grossly of two different structures: a core 20S proteasome with multicatalytic proteinase functions and an associated part possibly with a regulatory role. These two structures both consisted of multiple polypeptides with molecular masses of 21-31 and 35-110 kDa, respectively. The subunit multiplicity of the rat 26S proteasome closely resembled that of the human counterpart, showing only minor species-specific differences in certain components. The assembly of this multi-component complex was found not to involve a sulfhydryl bond. Electrophoretic peptide mapping with lysyl-endopeptidase indicated the non-identity of the multiple subunits of the 26S proteasome. From these structural and functional characteristics, the 26S proteasome, which is widely distributed in mammals, is suggested to be a new type of multi-molecular complex catalyzing the soluble energy- and ubiquitin-dependent proteolytic pathway.

Yotsuyanagi's theory is often quoted in the discussion of the etiology of congenital dilatation of the biliary duct (CDBD), but there has been no established etiology as yet. With particular reference to the relationship between anomalous arrangement of the pancreaticobiliary ducts and CDBD, Babbit collected 19 cases of CDBD. The authors also observed the anomalous arrangement in 10 of 24 cases of CDBD (42 percent). Analysis of 570 CDBD cases collected in Japan disclosed that the anomalous arrangement was present in 183 of them (33 percent), dilation of the intraheptic bile ducts in 236 (42 percent), and narrowing and malformation of the bile duct in the hepatic hilum in 58 (10 percent). The authors have proposed a new classification, including these morphologic anomalies of the whole pancreaticobiliary ductal system. This classification provides useful indices in selecting the surgical procedures. The effect of the anomalous arrangement was pathophysiologically studied on dogs. The static internal pressure of the dog pancreatic duct was 14.6 + or - 5.5 cm H2O, and that of the dog bile duct, 8.9 + or - 3.4 cm H2O. Puppies were then operated on by shunting the pancreaticobiliary ducts. As the result, the biliary tract was devastated by pancreatic juice, giving rise to similar pathologic changes to those clinically observed.

Addition of epinephrine to primary cultured adult rat hepatocytes stimulated their DNA synthesis dose-dependently, especially in presence of insulin and epidermal growth factor. This effect of epinephrine was strongly inhibited by an alpha 1-antagonist, prazosin, but not by a beta-antagonist, propranolol, and was also slightly inhibited by an alpha 2-antagonist, yohinbin. These results indicate that the stimulation of DNA synthesis of hepatocytes by epinephrine is mediated predominantly by an alpha 1-action. 12-o-Tetradecanoylphorbol-13-acetate (TPA) or Ca2+-ionophore A-23187 stimulated DNA synthesis of Swiss 3T3 cells, but did not induce DNA synthesis of hepatocytes either singly or in combination. The fact that pretreatment of hepatocytes with TPA caused down-regulation of the stimulatory effect of epinephrine on DNA synthesis of hepatocytes within 15 min suggested that the effect of epinephrine on hepatocytes is mediated by its alpha 1 receptor and that TPA activated protein kinase c in the hepatocytes. Addition of dibutyryl cGMP did not induce DNA synthesis of hepatocytes. Therefore, the alpha 1-action of epinephrine that induce stimulation of DNA synthesis of primary cultured adult rat hepatocytes was apparently not mediated by either activation of phospholipid-dependent protein kinase or Ca2+ mobilization. Possible alternative mechanism was discussed.

Congenital biliary dilatation (CBD) or choledochal cyst has previously been considered a rarity; however, the number of cases reported in the literature has been increasing. It is generally accepted that there is a predominance in Japanese, as more than one‐third of the cases are from Japanese literature.