Microheterogeneity of biliverdin reductase in rat liver and spleen: selective suppression of enzyme variants in liver by bromobenzene.

Recently we have reported the detection of multiple net-charge and molecular mass variants of biliverdin reductase in the rat liver. We now report an apparent selective change in the electrophoretic profile of the reductase variants in the liver by in vivo bromobenzene treatment (2 mmol/kg, sc, 24 h). Using two-dimensional electrophoresis and isoelectric focusing, one molecular mass species of the reductase (Mr 30,400) appeared to be selectively suppressed by bromobenzene treatment. This molecular mass species was the main component of two isoelectric focusing bands with pI6.23 and 5.91. The effect in vivo of bromobenzene could not be duplicated by in vitro experiments involving treatment of purified enzyme with bromobenzene in the presence of a NADPH-dependent microsomal drug metabolizing system. The phenomenon of multiplicity of the reductase was not limited to the liver. Multiplicity of the enzyme was detected also in the spleen; however, the pattern of composition of the reductase variants vastly differed from that of the liver. In the spleen, variants with pI 5.76, 5.61, and 5.48 were the prevalent forms; the variant with pI 6.23 was absent, and pI 5.91 was present in a minute amount. Further, bromobenzene did not affect the composition pattern of net-charge variants in this organ. Also, the splenic biliverdin reductase activity was refractory to in vivo bromobenzene treatment, whereas the liver reductase activity with both NADH and NADPH was altered by the treatment. The possible significance of the presence of multiple variants of biliverdin reductase and the change in their composition caused by bromobenzene is discussed.