Inositol pentaphosphate in fish red blood cells

Area of Science:

• Biochemistry
• Comparative Physiology
• Marine Biology

Background:

• Inositol pentaphosphate (IP5) is a known organic phosphate in avian erythrocytes.
• Its presence and function in non-avian species remain less understood.

Purpose of the Study:

• To investigate the presence and concentration of inositol pentaphosphate (IP5) in elasmobranch fish erythrocytes.
• To compare the organic phosphate profile of elasmobranch red cells with other vertebrates.

Main Methods:

• Erythrocytes were isolated from Squalus acanthias (spiny dogfish) and Narcacion nobiliana (torpedo ray).
• Concentrations of inositol pentaphosphate (IP5), ATP, and GTP were quantified using biochemical assays.
• The absence of 2,3-diphosphoglycerate was noted.

Main Results:

• Inositol pentaphosphate (IP5) was detected in the red blood cells of both spiny dogfish and torpedo ray.
• Mean IP5 concentrations were 0.36 µmol/mL and 0.24 µmol/mL, respectively.
• Adenosine triphosphate (ATP) was the predominant organic phosphate, while 2,3-diphosphoglycerate was absent.

Conclusions:

• Inositol pentaphosphate (IP5) is present in elasmobranch fish erythrocytes, expanding its known vertebrate distribution.
• The organic phosphate composition of elasmobranch red cells differs from mammals, lacking 2,3-diphosphoglycerate but containing IP5.
• Guanosine triphosphate (GTP) levels correlate with IP5 concentrations in these species.