PMID: 8463269Apr 5, 1993Paper

Regulation of heme oxygenase and metallothionein gene expression by the heme analogs, cobalt-, and tin-protoporphyrin.

The Journal of Biological Chemistry
A SmithW T Morgan

Abstract

Two heme analogs, cobalt- and tin-protoporphyrin (CoPP and SnPP, respectively) have been used to probe the heme-hemopexin interaction, hemopexin receptor binding, and the mechanism of regulation of heme oxygenase (HO) and metallothionein-1 (MT-1) gene expression by hemopexin. Both CoPP and SnPP are HO inhibitors and hemopexin binds SnPP (Morgan, W. T., Alam, J., Deaciuc, V., Muster, P., Tatum, F. M., and Smith, A. (1988) J. Biol. Chem. 263, 8226-8231) and CoPP. The association of CoPP with hemopexin produces characteristic changes in the absorbance spectrum of CoPP and quenches the intrinsic fluorescence of hemopexin. Binding of CoPP is tight (Kd ca. 3 x 10(-7) M) although of lower affinity than heme itself (Kd < pM); and CoPP binding, like heme, produces conformational changes in hemopexin shown by an increase in the molar ellipticity at 233 nm and affords protection from proteolysis of the hinge region between the two structural domains of hemopexin. The coordination of the central cobalt atom is predicted to be similar to that of heme and to involve His56 and His127 of rabbit hemopexin. Furthermore, CoPP-hemopexin, like SnPP-hemopexin, binds to the hemopexin receptor as shown by competitive inhibition studies with radioactiv...Continue Reading

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