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Characterization of Sheep Lacrimal-Gland Peroxidase and Its Major Physiological Electron Donor.

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Title Characterization of Sheep Lacrimal-Gland Peroxidase and Its Major Physiological Electron Donor.
 
Creator Majumder, Avijit
Chatterjee, Ratna
Adak, Subrata
Ghosh, Anil K
Mandal, Chhabinath
Banerjee, Ranajit K
 
Subject Structural Biology & Bioinformatics
 
Description A soluble sheep lacrimal-gland peroxidase was puriÆed to
apparent homogeneity. It had a native molecular mass of 75 kDa with a subunit molecular mass of 82 kDa and an isoelectric point of 6.5. Western blotting showed that it shares some of the enzyme antigenic determinants in common with other soluble peroxidases. The enzyme exhibits a Soret peak at 410 nm which is shifted to 431 nm by 5 equiv. of H#O# due to the formation of compound II. The latter is, however, unstable and gradually returns to the native state. The enzyme forms complexes with CN− andN$
− and is reduced by dithionite showing a characteristic
reduced peroxidase spectrum. Although the enzyme oxidizes I−, SCN− and Br− optimally at pH 5.5, 5.25 and 5.0 respectively, at physiological pH, it oxidizes I− and SCN− only. Since extracellular SCN− concentration is much higher than I−, SCN− may act as the major electron donor to the enzyme. The second-order rate constants for the reaction of the enzyme with H#O# (k+") and of compound I with SCN− (k+#) were 4¨10( M−"[s−" and 8.1¨10& M−"[s−" respectively. A plot of log Vmax. against pH yields a sigmoidal curve consistent with a single ionizable group on the enzyme with a pKa value of 5.75, controlling thiocyanate oxidation. In a coupled system with the peroxidase, H#O#, SCN−,
GSH, NADPH and glutathione reductase, peroxidase-catalysed
SCN− oxidation by H#O# could be coupled to NADPH consumption. The system is proposed to operate in äiäo for the eæcient elimination of endogenous H#O#.
 
Date 1996
 
Type Article
PeerReviewed
 
Format application/pdf
 
Identifier http://www.eprints.iicb.res.in/1021/1/BioJabhijit.pdf
Majumder, Avijit and Chatterjee, Ratna and Adak, Subrata and Ghosh, Anil K and Mandal, Chhabinath and Banerjee, Ranajit K (1996) Characterization of Sheep Lacrimal-Gland Peroxidase and Its Major Physiological Electron Donor. Biochemical Journal, 314. pp. 413-419.
 
Relation http://dx.doi.org/
http://www.eprints.iicb.res.in/1021/