Patterns of cystine reduction by fibroblasts from normal and cystinotic children
| Autor: | Stanton Segal, Dorothy Harris, Beatrice States |
|---|---|
| Rok vydání: | 1977 |
| Předmět: |
chemistry.chemical_classification
Cystinosis Cystine Glutathione Metabolism Fibroblasts medicine.disease Cell Line chemistry.chemical_compound Enzyme medicine.anatomical_structure Biochemistry chemistry Cell culture Pediatrics Perinatology and Child Health medicine Humans Fibroblast Oxidation-Reduction Intracellular |
| Zdroj: | Pediatric research. 11(5) |
| ISSN: | 0031-3998 |
| Popis: | Summary: The possibility that the enzymatic reduction of cystine involves a multi-enzyme system led to re-evaluation of cystine reduction by flbroblasts from normal and cystinotic patients. Lineweavcr- Burk plots of data with extracts of a normal cell line, representative of seven normal cell lines, under conditions of increasing cystine with variable levels of reduced glutathione (GSH) resulted in a two-limbed curve above 100 μM cystine. Two cell lines from children with nephropnthic cystinosis containing 1–6 μmol half-cystine/g protein gave a family of curves similar to those of the normal. With six fibroblast lines containing more than 6 μmol half-cystine/g protein, increasing cystine resulted in a family of lines without two-limbed curves. Plots of the data as activity against increasing cystine concentrations at ratios of cystine to GSH of 1:2 and 1:1 showed that two of the three lines from cystinotic subjects reduced cystine at a faster rate than the normal line. The third line from a cystinotic patient reduced cystine at a slightly slower rate when the substrate concentration in the assay was less than 80 μM cystine. When the cystine to GSH ratio was maintained at 2:1, normal cells showed a linear increase in the rate of cystine reduction up to 100 μM cystine, no increase in the rate between 100 μM and 200 μM cystine, and an increase again when the concentration of cystine was raised above 200 μM. Such a stepwise phenomenon was absent with six cell lines containing more than 6 μmol half-cystine/g cellular protein. A possible mechanism of control of cystine reduction is discussed. Speculation: A defect in the reductive mechanism of cystine metabolism has been suggested as a cause of cystinosis. Plots of the rate of cystine reduction with increasing cystine concentration at a cystine to glutathione ratio of 2:1 showed a pattern typical of a multiple enzyme system with extracts from normal cells. Since such a two-step configuration is not observed with extracts from cells containing high levels of intracellular cystine, the control of cystine reduction inherent in the complex multienzyme system in normal cells may be absent, altered, or defective in cells from cystinotic patients. This difference in the pattern of cystine reduction by cells from cystinotic patients could be due to either a primary or a secondary factor resulting in sequestration of cystine in cystinosis. However, many additional kinetic parameters, starting with delineation of the multistep enzyme system, remain to be investigated before a judgment can be made as to the role of this abnormal pattern in the storage of cystine by cells from cystinotics. |
| Databáze: | OpenAIRE |
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