Abstract
Fatty acid-binding proteins (FABPs) were purified from the kidneys of female and male rats and characterized by primary structure and histological distribution in the kidney. Two FABPs (14 and 15.5 kDa) were found in male rat kidney cytosol whereas only 14-kDa FABP could be recognized in female rat kidneys throughout the purification steps. The amino acid sequence of the 14-kDa FABP was identical to that of rat heart FABP deduced from the cDNA sequence (Heuckeroth, R. O., Birkenmeier, E. H., Levin, M. S., and Gordon, J. I. (1987) J. Biol. Chem. 262, 9709-9717). Structural analysis of the male-specific 15.5-kDa FABP identified this second FABP as a proteolytically modified form of alpha 2u-globulin, an 18.7-kDa major urinary protein of adult male rats (Unterman, R. D., Lynch, K. R., Nakhasi, H. L., dolan, K. P., Hamilton, J. W., Cohn, D. V., and Feigelson, P. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 3478-3482) which shares a common ancestry with a number of hydrophobic ligand-binding proteins such as serum retinol-binding proteins. Immunohistochemical investigation disclosed that heart-type FABP (14-kDa FABP) is localized in the cytoplasm of the epithelia of the distal tubules in both male and female rat kidneys whereas 15.5-kDa FABP immunostaining was observed predominantly in the endosomes or lysosomes of proximal tubules in male rat kidneys. These results suggest strongly the functional divergence of two FABPs in the rat kidney.
Highlights
Fatty acid-binding proteins (FABPs) were purified from the kidneys of female and male rats and characterized by primary structure and histological distribution in the kidney
Immunohistochemical investigation disclosed that heart-type FABP (14-kDa FABP) is localized in the cytoplasm of the epithelia of the distal tubules in both male and female rat kidneys whereas 15.5-kDaFABP immunostaining was observed predominantly in the endosomes or lysosomes of proximal tubules in male rat kidneys
One was a heart FABP-like protein (14-kDa FABP(m), "m" stands for male) and the other was the kidney FABP (15.5-kDa FABP) described by Fujii et al [21] and by Lam et aL(l9).On the other hand, female kidney cytosol yielded only the 14-kDa FABP species (14-kDa FABP(f), "f' for female), which was prepared by a slight modification of the procedure of Fujii et al [21]
Summary
Two species of FABP were purified from male rat kidneys t o homogeneity on SDS-PAGE by the procedure of Fujii et al [21] (data notshown). The amino acid could be unambiguously aligned with the cDNA-deduced secomposition of 14-kDa FABP(f) was similar to that of quence of rat heart FABP (Fig. 3). This demonheart FABP butclearly different from that of kidney FABP stratedthattheprimarystructure of 14-kDaFABP(f)is (datanotshown). Residue segment hadbeen removed [20].the molecular mass predicted from thseequence data for the processed a2,-globulin is 17.7 kDa,which isnotconsistentwiththe molecular mass of 15.5 kDa determined by SDS-PAGE This lower value for kidney FABP was confirmed by HPLC gel FIG.. These purified peptides were subjected to amino P -c 10- acid analysis (Table 4, miniprint) and sequence analysis. It is most likely that kidney FABP (15.5-kDa FABP) undergoes proteolytic processing in the carboxyl-terminal region as well asinthe amino-terminal region and loses the carboxyl-terminal 2- or 3-residue segment of the predicted sequence of a2,-globulin
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