Quantitation of plasma membrane fatty acid-binding protein by enzyme dilution and monoclonal antibody based immunoassay.
A plasma membrane fatty acid-binding protein (h-FABPpm) has been isolated from rat hepatocytes. Analogous proteins have also been identified in adipocytes, jejunal enterocytes and cardiac myocytes, all cells with high transmembrane fluxes of fatty acids. These 43 kDa, highly basic (pI = 9.1) FABPpm's appear unrelated to the smaller, cytosolic FABP's (designated FABP's) identified previously in the same tissues. h-FABPpm appears closely related to the mitochondrial isoform of glutamic-oxaloacetic transaminase (mGOT), and both the purified protein and liver cell plasma membranes (LPM) possess GOT enzymatic activity. From their relative GOT specific activities it is estimated that h-FABPpm constitutes approximately 2% of LPM protein, or about 0.7 x 10(7) sites per cell. A monoclonal antibody-based competitive inhibition enzyme immunoassay (CIEIA) for h-FABPpm is described; it yields an estimate of 3.4 x 10(7) h-FABPpm sites per hepatocyte. Quantitated by either method, h-FABPpm appears to be a highly abundant protein constituent of LPM.
Zhou
S L
SL
Department of Medicine (Division of Liver Diseases), Mount Sinai School of Medicine of the City University of New York, New York 10029.
Potter
B J
BJ
Stump
D
D
Sorrentino
D
D
Berk
P D
PD
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D001219:Aspartate Aminotransferases / Q000378:metabolism; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000032:analysis* / Q000276:immunology; D002462:Cell Membrane / Q000737:chemistry* / Q000201:enzymology; D002478:Cells, Cultured; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D007118:Immunoassay; D008099:Liver / Q000166:cytology; D051379:Mice; D008807:Mice, Inbred BALB C; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D009928:Organ Specificity; D051381:Rats
D000911:Antibodies, Monoclonal; D002352:Carrier Proteins; C082667:Fabp5 protein, mouse; C086936:Fabp7 protein, mouse; C490174:Fabp7 protein, rat; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D001219:Aspartate Aminotransferases