Ceruloplasmin

Ceruloplasmin, a protein from the a-globulin fraction of human plasma, is usually considered to be the major copper transport protein. However, it also catalyzes the oxidation of biogenic amines, including catecholamines, adrenaline, noradrenaline, dopamine, and the indoleamine 5-hydroxytrypta-mine (5HT). 

The assay for oxidation of these amines involves the use of any of the compounds listed above as the substrate and their separation from their respective products, aminochromes, by reversed-phase, ion-paired HPLC (ODS-Hypersil). The column was eluted isocratically using a mobile phase containing 50 mAf potassium phosphate buffer (pH 5.5), 2 mAf sodium heptanesulfonate, and methanol, at concentrations of 7.5 to 17.5% depending on the substrate. The detection was at 300 nm. 

Activity was assayed in a reaction mixture (1.2 mL final volume) containing the substrate and buffer. The reaction was started by the addition of the enzyme and, after incubation at 37°C for 45 minutes was terminated by the addition of a 15 mAf sodium azide solution. Samples were removed and injected directly onto the HPLC column for analysis. To generate products to be used as standards, oxidation of each of the amines to the corresponding aminochrome was carried out by incubation of the substrate with 30 mAf potassium hexacyanoferrate(IH) solution for 1 hour at room temperature. 

The enzyme was obtained from commercial sources or from human serum. 

Figive 9.124 Chromatogram obtained following incubation of adrenaline with ceruloplasmin. Peaks a, adrenochrome b, adrenaline. (From Richards, 1983.) 

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IV, a-l-proteinase inhibitor antithrombin III IgM ceruloplasmin a- and P-globutins a-tipoprotein albumin 5-10... 

Copper is one of the twenty-seven elements known to be essential to humans (69—72) (see Mineral nutrients). The daily recommended requirement for humans is 2.5—5.0 mg (73). Copper is probably second only to iron as an oxidation catalyst and oxygen carrier in humans (74). It is present in many proteins, such as hemocyanin [9013-32-3] galactose oxidase [9028-79-9] ceruloplasmin [9031 -37-2] dopamine -hydroxylase, monoamine oxidase [9001-66-5] superoxide dismutase [9054-89-17, and phenolase (75,76). Copper aids in photosynthesis and other oxidative processes in plants. 

Ceruloplasmin (from human blood plasma) [9031-37-2] Mr 134,000. This principle Cu transporter (90-90% of circulating Cu) is purified by precipitation with polyethylene glycol 4000, balchwise adsorption and elution from QAE-Sephadex, and gradient elution from DEAE-Sepharose CL-6B. Ceruloplasmin... 

CRP , complement , PLA2 , serum amyloid A , fibrinogen , c -acid glycoprotein , IL-1Ra , ceruloplasmin , ai-antichymotrypsin , LBP albumin , haptoglobin , IGF-1 , transferrin , u2-HS glycoprotein ... 

Table 50-2 summarizes the functions of many of the plasma proteins. The remainder of the material in this chapter presents basic information regarding selected plasma proteins albumin, haptoglobin, transferrin, ceruloplasmin, aj-antitrypsin, aj i roglobulin, the immunoglobulins, and the complement system. The lipoproteins are discussed in Chapter 25. 

Ceruloplasmin (contains Cu + albumin probably more important in physiologic transport of Cu T Corticosteroid-binding globulin (trans-cortin) (binds cortisol)... 

Ceruloplasmin Binds Copper, Low Levels of This Plasma Protein Are Associated With Wilson Disease... 

Ceruloplasmin (about 160 kDa) is an a2-globulin. It has a blue color because of its high copper content and... 

Copper is an essential trace element. It is required in the diet because it is the metal cofactor for a variety of enzymes (see Table 50—5). Copper accepts and donates electrons and is involved in reactions involving dismu-tation, hydroxylation, and oxygenation. However, excess copper can cause problems because it can oxidize proteins and hpids, bind to nucleic acids, and enhance the production of free radicals. It is thus important to have mechanisms that will maintain the amount of copper in the body within normal hmits. The body of the normal adult contains about 100 mg of copper, located mostly in bone, liver, kidney, and muscle. The daily intake of copper is about 2—A mg, with about 50% being absorbed in the stomach and upper small intestine and the remainder excreted in the feces. Copper is carried to the liver bound to albumin, taken up by liver cells, and part of it is excreted in the bile. Copper also leaves the liver attached to ceruloplasmin, which is synthesized in that organ. 

Another condition involving ceruloplasmin is aceru-loplasminemia. in this genetic disorder, levels of ceruloplasmin are very low and consequently its ferroxidase activity is markedly deficient. This leads to failure of release of iron from cells, and iron accumulates in certain brain cells, hepatocytes, and pancreatic islet cells. Affected individuals show severe neurologic signs and have diabetes mellitus. Use of a chelating agent or administration of plasma or ceruloplasmin concentrate may be beneficial. 

Ceruloplasmin contains substantial amounts of copper, but albumin appears to be more important with regard to its transport. Both Wilson disease and Menkes disease, which reflect abnormahties of copper metabohsm, have been found to be due to mutations in genes encoding copper-binding P-type ATPases. 

Solberg and co-workers have applied discriminate analysis of clinical laboratory tests combined with careful clinical and anatomic diagnoses of liver disease in order to determine which combinations of the many dozen liver diagnostic tests available are the bes t ( ). These authors found that the measurement of GPT, GMT, GOT, ALP and ceruloplasmin were the most useful enzymatic tests, when combined with other non-enzymatic tests such as the measurement of bilirubin, cholesterol, hepatitis-B associated Australian antigen, etc. Another group of highly useful enzymes, not discussed in this review, are those clotting factors and the enzyme cholinesterase which are synthesized by the liver cells. 

Lovstad, R.A. (1984). Catecholamine stimulation of copper-dependent haemolysis protective action of superoxide dismutase, catalase, hydroxyl radical scavengers and scrum proteins (ceruloplasmin, albumin and apotransferrin). Acta Pharmacol. Toxicol. 54, 340-345. 

Copper appears as the a2-globulin ceruloplasmin in the human body (Sarkar 1994). Deficiency of this protein in serum is characteristic of both Menkes and Wilson s diseases. Wilson s disease is an abnormal storage of Cu(II) in body tissues. Cu(II) in biological material can be determined by spectrophotometry or by FAAS, ceruloplasmin in serum by a spectrophotometric method. 

Ceruloplasmin is a protein for which many functions have been proposed - somewhat akin to Pirandello s Six Characters in Search of an Author, ceruloplasmin has long been a protein in search of a function. However, its importance in iron metabolism has been underlined by the observation of systemic iron loading in the tissues of patients with aceruloplasminaemia and other mutations in the ceruloplasmin gene. For further information on copper and iron interactions, see Chapter 12. 

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