Inactivation of phytochrome- and phycobiliprotein-chromophore precursors by rat liver biliverdin reductase.
1993; Elsevier BV; Volume: 268; Issue: 35 Linguagem: Inglês
10.1016/s0021-9258(19)74286-0
ISSN1083-351X
AutoresMatthew J. Terry, M D Maines, J. Clark Lagarias,
Tópico(s)Plant Gene Expression Analysis
ResumoThe phytochrome chromophore precursor, 3E-phytochromobilin, and the phycobiliprotein chromophore precursors, 3E-phycocyanobilin and 3E-phycoerythrobilin, are enzymatically converted to novel rubinoid products by purified rat liver biliverdin reductase.Phytochromobilin and phycocyanobilin are particularly good substrates for biliverdin reductase with K,,, and V , , values very similar to those of the natural substrate, biliverdin I X a .Phycoerythrobilin is the least preferred of the three bilin substrates.'H NMR spectroscopy of phycocyanorubin, the product of phycocyanobilin catalysis by biliverdin reductase, and comparison of absorption spectra of all three rubinoid products reveal that the C10 methine bridge is selectively reduced by biliverdin reductase without altering the A-ring ethylidene substituent.In vitro phytochrome assembly experiments demonstrate that the phytorubin products do not form photoactive adducts with recombinant apophytochrome.These results suggest that ectopic expression of biliverdin reductase in plants will prevent assembly of the functional photoreceptor and thus will potentially alter light-mediated plant growth and development.Biliverdin reductase (BVR)' catalyzes the reduction of biIiverdin IXa (BV) to bilirubin (BR) in the final step of heme catabolism in mammals and some species of fish (Singleton and Laster, 1965).A cytosolic enzyme with a molecular mass of approximately 33,000, BVR utilizes both NADPH and NADH for the reduction of BV (Kutty and Maines, 1981).At the protein level, BVR exhibits extensive microheterogeneity.At least 10 variants with different molecular mass and/or charge have been reported in mammals (Huang et al., 1989a).The pattern of expression of an individual BVR variant has been shown to be tissue dependent and can be modified by xenobiotic compounds (Huang et al., 1989b; Huang and
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