title: Analysis of two constitutive forms of microsomal heme oxygenase in different rat tissues.
abstract: OBJECTIVE
  To isolate and purify the heme oxygenase (HO) isoform in microsomal fractions of Sprague-Dawley rat liver and brain in order to understand the characteristics of the two constitutive forms and the mechanism of the occurrence of hyperbilirubinemia.
  
  
  METHODS
  After induction by hematin and phenylhydrazine, the rat liver and brain microsomal fractions were isolated and purified by DEAE-Sephacel and hydroxyapatite. Activity and the apparent molecular weight of the two isoforms [heme oxygenase 1 (HO-1) and heme oxygenase-2 (HO-2)] were measured. Kunming mice were used to prepare antiserum against purified liver HO-2. Rat liver HO-1 and brain HO-2 preparations were analyzed by the western immunoblotting technique.
  
  
  RESULTS
  Two isoforms were purified and identified in the treated rat liver, and HO-1 was the predominant form with a ratio of 2:1. In the native state, HO-2 activity was detectable but HO-1 activity was increased in response to hematin and phenylhydrazine, while HO-2 activity was fully refractory to these agents. The apparent molecular weights of HO-1 and HO-2 were about Mr 30000 and Mr 36000 under reducing conditions, respectively. In the untreated liver and treated brain, only one peak of HO activity exhibiting an elution profile similar to that of HO-2 of the treated liver was detected. The presence of an activity peak was not found in the elution profile at the region where the inducible isoform of HO (HO-1) was expected. The apparent molecular weight in treated brain preparation was identical to that of the purified liver HO-2. Cross-reactivity of HO-2 in the brain microsomal preparation was established, but a reactivity of HO-1 in the liver was not observed by western immunoblotting analysis when antiserum to liver HO-2 was applied.
  
  
  CONCLUSIONS
  Two constitutive forms of HO, designated as HO-1 and HO-2, exist in the treated rat liver. HO-1 is an inducible enzyme. In the treated rat brain only HO-2 exists and is a molecular entity similar to that found in liver. The two constitutive forms were different in molecular weight and in inducibility and immunochemical properties.
authors.affiliation: Zhen-Wei Xia, Yun-Zhu Li, Shun-Nian Chen, Xiao- Ming Ben, Shan-Chang Yu, Department of Pediatrics, Ruijin Hospital, Shanghai Second Medical University, Shanghai 200025, China.
authors.forename: Z W
authors.initials: ZW
authors.lastname: Xia
authors.affiliation: Zhen-Wei Xia, Yun-Zhu Li, Shun-Nian Chen, Xiao- Ming Ben, Shan-Chang Yu, Department of Pediatrics, Ruijin Hospital, Shanghai Second Medical University, Shanghai 200025, China.
authors.forename: Y Z
authors.initials: YZ
authors.lastname: Li
authors.affiliation: Zhen-Wei Xia, Yun-Zhu Li, Shun-Nian Chen, Xiao- Ming Ben, Shan-Chang Yu, Department of Pediatrics, Ruijin Hospital, Shanghai Second Medical University, Shanghai 200025, China.
authors.forename: S N
authors.initials: SN
authors.lastname: Chen
authors.affiliation: Zhen-Wei Xia, Yun-Zhu Li, Shun-Nian Chen, Xiao- Ming Ben, Shan-Chang Yu, Department of Pediatrics, Ruijin Hospital, Shanghai Second Medical University, Shanghai 200025, China.
authors.forename: Q X
authors.initials: QX
authors.lastname: Shen
authors.affiliation: Zhen-Wei Xia, Yun-Zhu Li, Shun-Nian Chen, Xiao- Ming Ben, Shan-Chang Yu, Department of Pediatrics, Ruijin Hospital, Shanghai Second Medical University, Shanghai 200025, China.
authors.forename: X M
authors.initials: XM
authors.lastname: Ben
authors.affiliation: Zhen-Wei Xia, Yun-Zhu Li, Shun-Nian Chen, Xiao- Ming Ben, Shan-Chang Yu, Department of Pediatrics, Ruijin Hospital, Shanghai Second Medical University, Shanghai 200025, China.
authors.forename: S C
authors.initials: SC
authors.lastname: Yu
keywords: Brain; Heme oxygenase; Hyperbilirubinemia; Liver