| 1. |
- Söderström, Mats, et al.
(författare)
-
Leukotriene C4 synthase : characterization in mouse mastocytoma cells
- 1990
-
Ingår i: Methods in Enzymology. - : Elsevier. - 0076-6879 .- 1557-7988. ; 187, s. 306-312
-
Tidskriftsartikel (refereegranskat)abstract
- The chapter presents a study on leukotriene C4 (LTC4) synthase, discussing the characterization in mouse mastocytoma cells. LTC4 is formed by conjugation of leukotriene A4 (LTA4) with glutathione (GSH). In biological systems, the reaction is catalyzed by a membrane-bound enzyme, leukotriene C4 synthase (EC 2.5.1.37). Cytosolic glutathione transferases, in particular, members of the class Mu, have been shown to catalyze formation of LTC4.The most efficient isoenzymes are transferase 6-6 isolated from rat brain, transferase 4-4 from rat liver, and transferase μ from human liver. The name leukotriene C4 synthase, used for the enzyme described in this chapter, has been adopted to distinguish the enzyme from the above glutathione transferases, which display broad substrate specificity. Reports from three groups of investigators have shown that LTC4 formation in rat basophilic leukemia cells is catalyzed by a membrane-bound enzyme. Leukotriene C4 synthase activity has been described and an enzyme partially purified from the microsomal fraction of guinea pig lung. The formation of LTC4 is especially high in mouse mastocytoma cells, the source from which LTC4 was first isolated. The partial purification of leukotriene C4 synthase from this source is described in the chapter.
|
|
| 2. |
- Söderström, Mats, et al.
(författare)
-
On the nature of leukotriene C4 synthase in human platelets
- 1992
-
Ingår i: Archives of Biochemistry and Biophysics. - : Elsevier. - 0003-9861 .- 1096-0384. ; 294:1, s. 70-74
-
Tidskriftsartikel (refereegranskat)abstract
- Leukotriene C4 is considered to play a major role in several important pathophysiological conditions, e.g., allergy, asthma, and shock. The present investigation demonstrates the presence in human platelets of a membrane-associated enzyme catalyzing the final step in the biosynthesis of leukotriene C4. This leukotriene C4 synthase was shown to be distinct from previously characterized "microsomal" and soluble glutathione transferases. The latter enzymes did not contribute significantly to the leukotriene A4 conjugating activity in platelets. As determined with leukotriene C4 synthase of a crude membrane fraction from human platelets, the Km value was 7 microM and the V value was 0.56 nmol x min-1 x mg-1 with leukotriene A4 as substrate. The enzyme was 20-fold more efficient with leukotriene A4 than with leukotriene A5 and 30-fold more efficient than with the unphysiological derivative leukotriene A4 methyl ester, as measured by the corresponding V/Km values; 14,15-leukotriene A4 was not a substrate. Platelets should be a useful source for the purification and further characterization of human leukotriene C4 synthase.
|
|
