Heme Oxygenase: Alternate Names

Heme oxygenase 1 (HO-1) is an ubiquitiously expressed stress response molecule and a member of the huge heat shock protein (HSP) superfamily. There are several alternate names associated with heme oxygenase 1 (HO-1). HO-1 has originally been described as heme α-methenyl oxygenase by Nakajima and colleagues ^{27, 28}. Independent investigations identified this enzyme as an inducible low-molecular weight stress protein, designated as p32 ^{50, 51}. Since HO-1 has initially been classified as being a heat shock protein in rats ⁵³, it may also be referred to as Hsp32. Alternate protein names also include heme oxygenase (decycling) 1, NP_002124.1, Heox, Hemox, and HMOX-1. HO-1 is encoded by a single-copy nuclear gene, HMOX1 clustered on chromosome 22q12.3. Gene aliases comprise HMOX1, HO-1, HSP32, HMOX1D, and bK286B10 (Table 2). One additional isoform was characterized in mammals, termed heme oxygenase 2 (HO-2). Both, HO-1 and HO-2 represent the expression products of different genes ⁸². A third variant described in rats only, HO-3, is supposed to be a pseudogene resulting from alternative splicing of the HMOX2 mRNA ⁴⁰ and referred to as Hmox2-ps1 and Hmox3, respectively. Expression of HO-3 could not be detected at the mRNA level in a genomic DNA-free liver library, nor at the protein level in kidney from rats ⁴⁰. Hmox3 represents a single-exon gene in rats which is absent in other mammals. A novel splice variant of HO-1 was recently identified in the cytoplasm of human malignant cells, termed 14 kDa HO-1 ⁶. Microbial HOs are referred to as ChuS and ChuW in E. coli ⁸³, HmuO in Corynebacterium spec. ⁴¹, Hmx1p in S. cerevisiae ⁴⁵ and Candida albicans ⁴⁶, PigA/HemO ⁸⁴ and BphO in Pseudomonas aeruginosa ⁸⁵, as well as HemO in Neisseria meningitides ^{43, 44}.  In the rhodophyte Rhodella violacea, HO is referred to as PbsA ¹³.