Highly homologous to find more histones, they have potent, broad-spectrum activity against Gram-negative bacteria, water molds and parasites (Richards et al., 2001 and Fernandes et al., 2002). Another example is the antimicrobial peptide hipposin from the skin mucus of Atlantic halibut (Hippoglossus hippoglossus L.) derived from the histone H2A ( Birkemo et al., 2003). Other antimicrobial proteins isolated from fish and having other primary functions include apolipoproteins A-I and A-II, present in skin or serum of carp (Cyprinus carpio) and active against some fish bacterial pathogens ( Concha et al., 2004). These proteins with other well established
functions appear to be recruited to a second antimicrobial role in nature. In the present work we purified and identified the fraction of the P. cf henlei mucus responsible for antimicrobial activity against E. coli, M. luteus and C. tropicalis. The purified PcfHb exhibited a lower MIC against gram-negative bacteria and higher against gram-positive bacteria and fungi. The MIC values were in the same range as well-characterized peptide fragments from bovine hemoglobin ( Adje et al., 2011) and antimicrobial peptides including pardaxins and hipposins ( Oren and Shai, AZD9291 cell line 1996 and Birkemo et al., 2003). Interestingly, the partial sequence alignment of PcfHb with several hemoglobin β-chain of different species,
demonstrated a high degree of conservation of certain amino acids ( Table 1). Some factors could explain the surprising antimicrobial activity of fragments of hemoglobin. One possibility is that the heme moiety
could act either as an iron chelator or as an oxidant, leading to damage of the bacterial and fungal cell walls. Parish et al. (2001) working with isolated chains of hemoglobin identified that the isolated C-X-C chemokine receptor type 7 (CXCR-7) β chain without heme exhibited activity on tested organisms, supporting the hypothesis that the heme plays no role in the antimicrobial activity and that subunit separation leads to enhanced activity. Thus, although the hemoglobin tetramer is only negligibly active against two gram-positive organism, the activity of the isolated β globin chain is greatly enhanced. In the case of β+heme, antimicrobial activity was observed against two of the bacterial targets but not on C. albicans. The results with isolated subunits indicate that tetramer dissociation exposes additional bioactive peptidic surfaces. Even though the tested microorganisms do not affect freshwater fish such as stingrays, proteins homologous to hemoglobin are also present in the microsomes of gill cells from a number of teleosts including Mozambique tilapia, Oreochromis mossambicus (Peters), rainbow trout, common carp, Cyprinus carpio L., European eel, Anguilla anguilla (L.), elephant fish, Gnathonemus petersii (Günther) ( Stekhoven et al., 2004) as well the presence of a family of AMPs derived from Hb-β present in the skin and gill epithelium of channel catfish ( Ullal and Noga, 2010).