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Biomedical subjects

T B Christensen

Publications and source records attributed to T B Christensen.

At least 37 records · Page 2Linked to original sources
PubMed1992

Cisplatinum dose dependent response in germ cell cancer evaluated by tumour marker modelling.

This study presents an analysis on longitudinal tumour marker series in twenty-two patients with non-seminomatous germ cell cancers treated with cisplatinum (DDP) based combination chemotherapy. Series of alphafoetoprotein (AFP), human chorionic gonadotrophin (HCG) and lactate dehydrogenase (LDH) were analyzed applying a dynamic mathematical marker model. The model analysis provided quantitated values for growth rate and treatment response in the marker producing cells. The analysis showed that LDH had to be above 2,000 U/l to be a trustworthy tumour marker. HCG producing cells tended to grow faster than AFP producing cells, and were 3-5-fold more sensitive to the chemotherapy given than AFP producing cells. Treatment response versus DDP dose appeared to be bi-phasic, but with no significant change in treatment efficiency within the given range of DDP doses.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1985

Further characterization of human eosinophil peroxidase.

The large and the small subunits (Mr 50 000 and 10 500 respectively) of human eosinophil peroxidase were isolated by gel filtration under reducing conditions. The subunits were very strongly associated but not apparently cross-linked by disulphide bridges. During storage, the large subunit tended to form aggregates, which required reduction to dissociate them. Amino acid analysis of the performic acid-treated large subunit showed the presence of 19 cysteic acid residues. The small subunit of eosinophil peroxidase had the same Mr value as the small subunit of myeloperoxidase. However, although these subunits have very similar amino acid compositions, they showed different patterns of peptide fragmentation after CNBr treatment. The carbohydrate of eosinophil peroxidase seemed associated exclusively with the large subunit and comprised mannose (4.5%, w/w) and N-acetylglucosamine (0.8%, w/w). The far-u.v.c.d. spectrum of the enzyme indicated the presence of relatively little ordered secondary structure.

Amino Acids↗
PubMed1985

Uptake and degradation of bovine testes beta-galactosidase by parenchymal and nonparenchymal rat liver cells.

The plasma half-life of beta-galactosidase in rat was about 1.5 min. Ten minutes after in vivo injection, 45% of the enzyme was recovered in liver, with hepatocytes and endothelial cells as the predominant cell types responsible for uptake. In vitro uptake of beta-galactosidase in hepatocytes and nonparenchymal liver cells was saturable, Ca2+-dependent and it could be partly inhibited by mannose or alpha-methyl-mannoside.

Animals↗
PubMed1984

Effect of dextran and modified dextrans on the uptake and degradation of beta-galactosidase in isolated liver cells.

Conjugation of beta-galactosidase with either dextran, methylated dextran or acetylated dextran had only a small effect on uptake of the enzyme in isolated rat parenchymal and nonparenchymal liver cells. Conjugation of beta-galactosidase with dextran or the modified dextrans, reduced the intracellular degradation of the enzyme by up to about 45%. Methylated dextran had less effect than unmodified dextran or acetylated dextran on reducing the intracellular degradation of beta-galactosidase.

Animals↗
PubMed1983

Enhanced stability of beta-galactosidase in parenchymal and nonparenchymal liver cells by conjugation with dextran.

In order to enhance the stability of beta-galactosidase, we conjugated the enzyme with dextran T-10 (Mr approx. 10 000). The conjugate contained 9-10 mol dextran/mol protein (beta-galactosidase, Mr 68 000), and the specific activity retained after conjugation was 90 +/- 4% (n = 3) of the initial activity. Uptake and degradation of native and conjugated beta-galactosidase in isolated hepatocytes and nonparenchymal liver cells was studied. There was a marked increase in stability against degradation in both cell types when beta-galactosidase was conjugated with Dextran. The degradation of dextran-conjugated enzyme was reduced by 35% in hepatocytes and by 43% in nonparenchymal cells, after 80 and 40 min, respectively, as compared with the free enzyme. However, there was insignificant difference between the uptake of native and conjugated enzyme into the liver cells. Upon intravenous infusion into rats, native and conjugated enzyme were cleared from plasma with only a slight difference in the clearance rate. The observed stability of dextran-conjugated beta-galactosidase towards cellular degradation was in accordance with the in vitro experiments. The conjugate showed marked thermal stability at 50 degrees C and enhanced resistance towards proteolysis by the broad specific protease subtilopeptidase A. This demonstrates that dextran conjugation may be used as a means of stabilizing lysosomal enzymes for therapeutic purposes.

Animals↗
PubMed1983

Effect of dextran and dextran modifications on the thermal and proteolytic stability of conjugated bovine testis beta-galactosidase and human serum albumin.

In order to study carbohydrate-induced protein stabilization bovine testis beta-galactosidase and human serum albumin were conjugated with dextran, partially acetylated dextran and partially methylated dextran. The conjugates and the free proteins were compared with respect to thermal stability at 50 degrees C and resistance to proteolytic digestion by subtilopeptidase A. Both beta-galactosidase and serum albumin were stabilized by conjugation with polysaccharide. However, higher stability was achieved by conjugating the proteins with the hydrophilic polysaccharides, dextran and acetylated dextran, than by conjugation with the hydrophobic polysaccharide, methylated dextran. The results are discussed in relation to possible explanations of carbohydrate-induced protein stabilization.

Animals↗
PubMed1976

On the significance of the carbohydrate moieties of bovine prothrombin for clotting activity.

Purified bovine prothrombin has been treated with different mixtures of glycosidases. Upon incubation of the prothrombin for 30 h with a combination of neuraminidase, alpha- and beta-galactosidase and beta-N-acetylglucosaminidase in 4 mM diisopropylfluorophosphate at pH 5.3 and 30 degrees C, about 70% of the carbohydrates were removed without affecting the coagulation activity. All the sialic acid and about half of the mannose, galactose and glucosamine residues were removed by this treatment.

Acetylglucosamine↗
PubMed1976

Chemical analysis of a sulphated macromolecule isolated from rabbit submandibular gland.

Chemical analysis of a sulphated macromolecule isolated from the rabbit submandibular gland showed that about 70 per cent of the dry weight could be accounted for in terms of amino acids of which the acidic amino acids, proline and alanine were the most abundant. Total carbohydrate was 11%. Galactose was the main neutral sugar but galactosamine, glucosamine, neuraminic acid, glucose and mannose could also be demonstrated. Sulphate accounted for 1,4%. No uronic acid was found. The data indicate that the sulphated macromolecule from the rabbit gland is in fact a sulphated glycoprotein.

Amino Acids↗
PubMed1975

Studies on the structure and properties of the lectins from Abrus precatorius and Ricinus communis.

The amino acid composition of the isolated A- and B-chains of the toxic lectins abrin and ricin was determined and compared. Even though the two toxins originate from widely different plants, statistical analysis of the amino acid content indicates extensive homologies in the amino acid sequence of the 4 chains. The intact lectins contain no free SH-groups whereas the isolated A- and B-chains contain close to one free SH-group each. The results indicate that in both toxins the A- and B-chains are connected by a single S-S bond. The B-chains of abrin and ricin contain similar amounts of mannose and glucosamine. The A-chain of ricin also contains some carbohydrate, whereas the A-chain of abrin appears not to be a glycoprotein. The non-toxic abrus and ricinus agglutinins contain more carbohydrate than abrin and ricin. The isoelectric points of the different lectin preparations were measured by isoelectrofocusing. The intact lectins are much more resistant to heat, freezing and chemical treatments than the isolated A- and B-chains. The intact lectins are also very resistant to treatment with proteolytic enzymes, whereas the isolated chains are easily digested. Evidence indicating that the toxins and their chains undergo extensive conformational changes upon reduction of the S-S bond is discussed.

Abrin↗
PubMed1975

IgM molecules with and without J chain in serum and after purification, studied by ultracentrifugation, electrophoresis, and electron microscopy.

IgM molecules in pure IgM preparations and in the corresponding sera from three patients with Waldenström's macroglobulinemia have been studied by analytical ultracentrifugation, rate zonal ultracentrifugation, agarose-polyacrylamide gel electrophoresis, and electron microscopy. One of the IgM preparations was without J chain, while the two others contained J chain. The experiments revealed that IgM with J chain consisted of pentameric molecules; whereas in IgM preparations without J chain the dominating molecules were hexamers, but also pentamers, tetramers, and even smaller molecules were found. In both types of IgM the molecules formed a wide range of aggregates, which were usually more abundant in the purified IgM than in serum. Some of the aggregates were kept together by noncovalent forces only.

Electrophoresis, Polyacrylamide Gel↗