| الملخص: |
Cysteine conjugate β-lyase (β-lyase) was purified to electrophoretic homogeneity from the kidney cytosol of male Wistar rats. The highly purified enzyme exhibited a monomeric molecular weight of 50,000 daltons and was active in the the α-β elimination of cysteine conjugates including S-(1,2-dichlorovinyl)-L-cysteine (DCVC), S-(1,1,2,2-tetrafluoroethyl)-L-cysteine (TFEC) and S-(2-benzothiazolyl)-L-cysteine (BTC), particularly towards DCVC and TFEC. The purified enzyme also exhibited glutamine transaminase K activity with L-phenylalanine and α-keto-γ-methiolbutyrate as substrates. An antibody was raised to the purified rat protein in sheep, and the crude immune serum affinity purified, yielding a specific antibody that recognised only the β-lyase protein in whole kidney homogenates. Immunocytochemical studies on rat kidney sections stained with the purified antibody revealed that the cytosolic β-lyase enzyme was mainly localised in the pars recta of the proximal tubule in untreated rats. This localisation is coincident with the site-specific kidney necrosis produced by hexachloro-1,3-butadiene (HCBD), indicating that the tissue localisation of β-lyase in the proximal tubule plays an important role in determining the specific nephrotoxicity produced by halogenated alkenes such as HCBD in the rat. The marked sex difference in rat susceptibility to HCBD was investigated and studies revealed that the female rat has significantly higher glutamine transaminase K activity than the male; however, no differences were noted between β-lyase enzyme activity, or location, in the proximal tubules of male and female rat kidney. The different pattern of nephrotoxic damage produced by nephrotoxic S-conjugates in species other than the rat was also examined by measuring renal β-lyase and transaminase activity and content in several species. Although, both β-lyase and transaminase activity was detected in all the species studied, renal β-lyase protein content and localisation could not be assessed due to the lack of reactivity between the affinity purified rat renal cytosolic β-lyase antibody and any species other than the rat. Consequently the results obtained herein provide no firm explanation for the different pattern of nephrotoxic damage produced by halogenated alkenes such as HCBD in species other than the rat. |
