Striped mullet (Mugil cephalus) hemoglobin system: multiplicity and functional properties

Abstract

The most frequent (90%) phenotype of the hemoglobin system of M. cephalus presented two major hemoglobins, the more anodal HbI accounting for approximately 70% of the total. The two hemoglobin components separated by ion-exchange chromatography were analyzed by reverse-phase HPLC and electrospray ionization-mass spectrometry which revealed a more complex pattern: HbI consists in four different globins, two β (named β1 and β3) and two co-eluting α chains (α1 and α2); HbII consists in three globins, one β chain (named β2) and the same α1 and α2 present in HbI. The oxygen-binding properties of both hemoglobin components purified by DEAE cellulose were almost identical to those of the hemolysate: stripped hemoglobin showed a large Bohr effect which was enhanced by chloride ions and, at a larger extent, by organic phosphates which, at acidic pH values gave rise to the Root effect. A series of oxygen-binding experiments at increasing GTP concentrations was carried out in order to compare GTP-binding activities in the absence and presence of physiological amounts of chloride. The results indicated that hemoglobin do have two sites for GTP binding. In the absence of chloride, the two sites cannot be discriminated, whereas in the presence of chloride, a competition between the two anions occurred for both GTP-binding sites. The presence of multiple hemoglobin components with identical properties confirms that hemoglobin heterogeneity that often occurs in fish cannot be only explained as an evolutionary response to the physiological and/or environmental needs of the species.

Evolution of Hemoglobin Genes in Codfishes Influenced by Ocean Depth

“… 33 ). On the other hand, in mullets no connection was found between Hb multiplicity and temperature variability 34 . Thus, the adaptive role of the size of the Hb repertoire in different codfishes may not be obvious.…”

Acclimation to prolonged hypoxia alters hemoglobin isoform expression and increases hemoglobin oxygen affinity and aerobic performance in a marine fish

“…We instead chose to explore the hypothesis that differential regulation of specific Hb components may coincide with increased oxygen affinity during hypoxia acclimation. It has been previously hypothesized that species with multiple Hbs acting in concert would be better suited to tolerate environmental perturbation 1 , 30 – 32 ; however, the physiological support for this is mixed 6 , 7 , 10 , 30 . But previous work has primarily focused on temperature, with relatively less work focusing on prolonged hypoxia acclimation 3 , 5 , 33 , 34 .…”

“…While Hb multiplicity in fish is well known and wide spread, the physiological implication of multiple isoHbs is unclear. In species such as the striped mullet ( Mugil cephalus ) 6 and gilt-head bream ( Sparus aurata ) 15 distinct isoHbs have almost identical functional properties. Conversely, Japanese eel ( Anguilla japonica ) express at least two functionally distinct Hb pools 7 , and acclimation to varying temperatures has also been demonstrated to differentially regulate isoHbs in several species 1 , 16 , 17 .…”

Molecular characterization, phylogenetic analysis and expression profiling of myoglobin and cytoglobin genes in response to heat stress in channel catfish Ictalurus punctatus

“…Teleost globins, such as Hb, myoglobin (Mb) and cytoglobin (Cygb), have been demonstrated to be responsible for oxygen circulation in vivo and waste gas expiration (Roesner et al, 2006;Olianas et al, 2011;Tiedke et al, 2011). The hb gene is ubiquitously expressed in all tissues with especially high levels of expression in blood, spleen and kidney; it is mainly in charge of oxygen and waste gas transportation (Jensen, 2007;Weber et al, 2010).…”