Comparative Biochemistry and Physiology Part B 124 (1999) 147 – 155 The Antarctic toothfish (Dissostichus mawsoni ) lacks plasma albumin and utilises high density lipoprotein as its major palmitate binding protein Victoria J. Metcalf *, Stephen O. Brennan, Peter M. George Molecular Pathology Laboratory, Department of Pathology, Christchurch School of Medicine, Uniersity of Otago, Christchurch, New Zealand Received 23 November 1998; received in revised form 26 February 1999; accepted 3 March 1999 Abstract Plasma from the Antarctic toothfish, Dissostichus mawsoni, a member of the advanced teleost Nototheniidae family, was analysed. Agarose gel electrophoresis showed a major diffuse anionic protein that bound [ 14 C]palmitic acid but not 63 Ni 2 + , and two more cationic proteins that bound 63 Ni 2 + but not palmitate. Oil Red O staining following cellulose acetate electrophoresis indicated that the palmitate binding protein was a lipoprotein. Two-dimensional electrophoresis showed that this palmitate binding band was composed of three proteins with M r of 11, 30, and 42 kDa, without any trace of material at 65 kDa, the mass of albumin. N-terminal sequencing of the palmitate binding band gave a major sequence of DAAQPSQELR-, indicating a high degree of homology to apolipoprotein A-I (apo-AI), the major apolipoprotein of high density lipoprotein (HDL). N-terminal sequencing of the major nickel binding band produced a sequence with no homology to albumin. When ultracentrifugation was used to isolate the lipoproteins from Antarctic toothfish plasma, the palmitate binding protein was found solely in the lipoprotein fraction. In competitive binding experiments, added human albumin did not prevent palmitate binding to toothfish HDL. In conclusion, there is no evidence for albumin in Antarctic toothfish plasma and HDL assumes the role of fatty acid transport. © 1999 Elsevier Science Inc. All rights reserved. Keywords: Albumin; Antarctic toothfish; Apo-AI; Apo-AIV; Fatty acid; High density lipoprotein (HDL); Palmitate; Protein sequence www.elsevier.com/locate/cbpb 1. Introduction The waters around Antarctica are constantly at sub- zero temperatures and have been since the formation of the continental ice sheet 10–15 mya (million years ago) [29]. The Antarctic Ocean is characterised by little temperature fluctuation, high water viscosity, and in- creased oxygen solubility. Despite this inhospitable marine environment, over 1% of the world’s fish species are found in Antarctic waters [19,20], with more than 50% of Antarctic fish species belonging to the Per- ciformes suborder Notothenioidei [4]. The Order Per- ciformes was the most recent teleost order to evolve, making species of the suborder Notothenioidei among the most phyletically derived of fish. The formation of the Antarctic Convergence current resulted in the isola- tion of the southern ocean 23–30 mya [21]. The fishes of the suborder Notothenioidei are thought to have evolved in situ as the Antarctic continent moved south and the surrounding ocean cooled. The notothenioids found in the Antarctic Ocean are characterised by the presence of antifreeze glycopep- tides (AFGPs), while those species with habitats outside the Convergence current, such as the earliest notothe- nioids, the Bovichtidae family, do not possess AFGPs [4,20]. The AFGP genes evolved from a pancreatic trypsinogen gene [13], with the multiple isoforms collec- tively maintained at an extremely high plasma concen- tration of 30–35 mg ml -1 [15,16]. Another notable characteristic of the notothenioids is a decrease in * Corresponding author. PO Box 4345, Christchurch; Tel.: +64-3- 3640548; fax: +64-3-3640545. E-mail address: victoria.metcalf@chmeds.ac.nz (V.J. Metcalf) 0305-0491/99/$ - see front matter © 1999 Elsevier Science Inc. All rights reserved. PII:S0305-0491(99)00051-6