Anatol G. Morell

Membrane glycoproteins and recognition phenomena

Abstract Information encoded in specific sugar residues o f membrane glycoproteins exerts a profound effect on cellular reactivity.

THE INCORPORATION OF COPPER INTO CERULOPLASMIN IN VIVO: STUDIES WITH COPPER64 AND COPPER67

The hypothesis that ceruloplasmin exchanges its copper for ionic copper in vivo was tested, by means of ceruloplasmin labeled with copper-64 and copper- 67, in two patients with Wilsons disease and in two control subjects. No indication of exchange was found in any of three different experiments. It appears that copper is incorporated into the ceruloplasmin molecule in vivo only at the time of synthesis of the protein and not through exchange. A corollary of these results is that copper is a lifelong label of a ceruloplasmin molecule so that radioactive copper may be used for the determination of the turnover of ceruloplasmin and ceruloplasmin copper. The amount of copper incorporated daily into ceruloplasmin in a control subject corresponds closely to the amount of copper absorbed from the dietary intake. (auth)

Lysosomal Defect of Hepatic Copper Excretion in Wilson's Disease (Hepatolenticular Degeneration)

After administration of 64Cu, striking differences were revealed in the copper content, specific activity, and protein binding of copper in the subcellular pools of hepatic copper in a woman with Wilsons disease compared with a control subject. None of the subcellular pools in the control subject could be identified as the source of the biliary copper, but the very low specific activity of 64Cu in lysosomes of the patient with Wilsons disease was virtually identical to that of the common duct bile and markedly different from all other subcellular pools. This suggested that lysosomes might be the source of biliary copper and that a lysosomal defect might account for the diminution of biliary copper excretion and the consequent hepatic accumulation of the metal in patients with Wilsons disease.

The existence of a second route for the transfer of certain glycoproteins from the circulation into the liver.

Abstract Oligosaccharide chains of agalactoorosomucoid, α 1 -acid glycoprotein from which sialic acid and galactose have been sequentially removed, terminate in N-acetylglucosaminyl residues. This protein is rapidly transferred from the circulation into the liver by a route distinct from that previously demonstrated for a number of galactosyl terminating glycoproteins.

Systemic Absorption of Intrauterine Copper

A comparison of the various effects, in rats, of intrauterine insertion of copper-64 or copper-67 wire with the effects of intraperitoneal injection of copper sulfate solutions has shown that copper ions, dissolved from the wire, are locally active contraceptively and, in part, systemically absorbed.

Heterogeneity of Human Ceruloplasmin

Subfractionation of purified human ceruloplasmin, prepared from plasma of 9109 donors, has been carried out by chromatography on columns of diethylaminoethyl cellulose and hydroxylapatite. Electrophoretic analyses of these subfractions on starch gels, at pH 8.5 and 5.7, reveal the presence of at least four ceruloplasmins, two of which appear to differ in histidine content.

[87] A membrane receptor protein for asialoglycoproteins

Publisher Summary Specific receptor sites have been identified on hepatic plasma membranes that appear to be involved in the catabolism of plasma glycoproteins by virtue of their ability to bind selectively to asialoglycoprotein, i.e., glycoproteins from which the terminal sialic acid residues have been removed. These receptors have been solubilized from particulate liver preparations by extraction with the nonionic detergent Triton X-100 3 and further purified by affinity chromatography on a column of Sepharose to which asialo-orosomucoid has been covalently attached. Binding of the receptor protein to the immobilized ligand occurs at a neutral or slightly alkaline pH and has an absolute requirement for calcium; elution is accomplished either by reducing the pH to between 5.6 and 6.4 or by addition of the calcium chelator EDTA. Excess Triton X-100 can be readily removed, prior to elution of the receptor by washing the column with a neutral, calcium-containing, aqueous buffer.

Solubilization of hepatic binding sites for asialo-glycoproteins

Abstract A lyophilized preparation of a particulate fraction of rabbit liver homogenate exhibits specific binding affinity for a desialylated glycoprotein comparable to that found in rat liver plasma membranes. Treatment of this preparation with Triton X-100 solubilizes the receptor sites which are capable of retaining their specific binding activity in solution.

A rapid screening test for deficiency of plasma ceruloplasmin and its value in the diagnosis of Wilson's disease

Abstract A spot test is described which makes it possible to determine simply and with a satisfactory degree of certainty whether or not an individual has more or less than about 20 mg. of ceruloplasmin per 100 ml. of plasma or serum. The test should be applicable as a screening procedure to detect asymptomatic children with hypoceruloplasminemia in whom Wilsons disease may subsequently develop. Based on current knowledge, and with available pharmacologic agents, it may be practicable to prevent or delay the onset of symptoms and signs of Wilsons disease in such children. The test may also be used in the study of patients suspected of having Wilsons disease.

534 HEPATIC BINDING PROTEIN (HBP)-ONTOGENY OF THE ASIALOGLYCOPROTEIN RECEPTOR IN MICE

Serum asialoglycoproteins bind to the hepatocyte receptor HBP, are internalized and catabolized in lysosomes. Human fetal liver is said to lack receptor, while adult liver contains 10 ug/gm determined as cpm I125-asialoorosomucoid(ASOR) substrate bound.Female CD-1 mice produced eight timed litters of 10-14 pups, which were killed between birth and 23 days of age. Seven females were killed during pregnancy, immediately after delivery and during suckling. Virgin female and male mice were studied at 6 weeks and 4 months of age. After cervical dislocation, liver was removed, frozen at-70°C and assayed within 30 days. Aliquots of liver were homogenized, incubated with I125-ASOR (prepared from pooled human sera) in 0.1M Tris pH7.9 containing 0.1% Triton X-100 at 30° for 10 minutes. HBP-I125 ASOR complex was precipitated with 10% polyethyleneglycol, filtered, washed and precipitate cpm determined. Binding could be inhibited by specific anti-rat HBP antibody.Fetal HBP activity was detectable one day prior to birth and rose to a plateau value at 5 days of age with no further increase to 6 weeks. In the last five days of pregnancy, maternal liver HBP activity was increased 150%. These data suggest fetal liver HBP is not involved in fetal glycoprotein metabolism, but HBP is inducible in maternal liver during pregnancy and in pups in the perinatal period. (NIAMDD Grant AM 17702).