A fatty acid-binding protein and a protein disulphide isomerase-related protein expressed in urochordate gonad cytosol Brian M. Cavagnari a , Marcos TatiaÂn b , Ricardo J. Sahade b , Graciela B. Esnal b , Jose A. Santome a, * a Instituto de QuõÂmica y FisicoquõÂmica Biolo Âgicas (IQUIFIB), Facultad de Farmacia y BioquõÂmica, UBA-CONICET, Junin 956, 1113 Buenos Aires, Argentina b Departamento de Cs. Biolo Âgicas, Facultad de Cs. Exactas y Naturales, UBA-CONICET, 1428 Buenas Aires, Argentina Received in revised form 14 February 2000; accepted 15 February 2000 Abstract 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 vertebrate/ invertebrate split, only the heart fatty acid-binding protein has been reported for invertebrates. In an attempt to shed light on this apparent inconsistency the presence of the other two branch members was investigated in the Urochordata Molgula pedunculata, an ascidian species close to vertebrates. The mantle-, gonad- and digestive tube- cytosolic fractions, obtained by centrifugation at 106,000 g, were incubated separately with [1- 14 C]palmitic acid and then fractionated on a Sephadex G-75 column. In the case of gonads and digestive tube, radioactive peaks corresponding to a molecular mass of 14±16 kDa, characteristic of fatty acid-binding proteins, were detected. When the experiment was performed on the mantle, this peak showing fatty acid binding capacity was absent. Western Blot of the radioactive 14±16 kDa Sephadex fraction from the urochordate gonad cross-reacted with rat liver fatty acid-binding protein anti-serum but did not do so with anti-rat intestinal, adipocyte or heart fatty acid-binding protein antisera. The material from the digestive tube was not recognized by any of the antisera. The most abundant protein in said 14±16 kDa fraction was a protein disulphide isomerase-related protein. Its partial amino acid sequence was determined. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Fatty acid-binding proteins; Protein disulphide isomerase; Sequence comparison; Molgula pedunculata; Urochordates 1. Introduction Cytosolic fatty acid-binding proteins (FABPs) were ®rst described in 1972 [1] and, over several The International Journal of Biochemistry & Cell Biology 32 (2000) 769±777 1357-2725/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S1357-2725(00)00014-5 www.elsevier.com/locate/ijbcb * Corresponding author. Tel.: +54-011-4508-3651; fax: +54-011-4508-3652. E-mail address: santome@qb.yb.uba.ar (J.A. SantomeÂ).