A fatty acid-binding protein and a protein disulphide isomerase-related protein expressed in urochordate gonad cytosol

Despite the evolutionary-tree data suggesting that gene duplication leading to the divergence of the three branches which heart, liver and intestinal fatty acid-binding proteins belong to must have occurred before the vertebr ate/invertebrate split, only the heart fatty acid-binding protein has been reported for invertebrates. In an attempt to shed light on this apparent in consistency the presence of the other two branch members was investigated i n the Urochordata Molgula pedunculata, an ascidian species close to vertebr ates. The mantle-, gonad- and digestive tube-cytosolic fractions, obtained by centrifugation at 106,000 g, were incubated separately with [1-C-14]palm itic acid and then fractionated on a Sephadex G-75 column. In the case of g onads and digestive tube, radioactive peaks corresponding to a molecular ma ss of 14-16 kDa, characteristic of fatty acid-binding proteins, were detect ed. When the experiment was performed on the mantle, this peak showing fatt y acid binding capacity was absent. Western Blot of the radioactive 14-16 k Da Sephadex fraction from the urochordate gonad cross-reacted with rat live r fatty acid-binding protein anti-serum but did not do so with anti-rat int estinal, adipocyte or heart fatty acid-binding protein antisera, The materi al from the digestive tube was not recognized by any of the antisera. The m ost abundant protein in said 14-16 kDa fraction was a protein disulphide is omerase-related protein. Its partial amino acid sequence was determined. (C ) 2000 Elsevier Science Ltd. All rights reserved.