Localization of the Heme–Binding Protein in the Cytoplasm and of A Heme–Binding Protein–Like Immunoreactive Protein in the Nucleus of Rat Liver Parenchymal Cells: Immunocytochemical Evidence of the Subcellular Distribution Corroborated by Radioimmunoassay and Immunoblotting

Abstract

The abundant heme-binding protein of the liver, probably identical with Z-protein or liver fatty acid-binding protein, has an apparent molecular weight of 14,000 Da and is presumably involved in the intracellular transport of a variety of compounds. The cellular and subcellular distribution of HBP in the liver was studied in adult male and female rats by postembedding immunocytochemistry using the protein A-gold technique. By light microscopic examination heme-binding protein is present exclusively in parenchymal cells and not found in the sinusoidal lining cells or other cells in portal tracts. Immunoreactivity for heme-binding protein is uniformly strong throughout the liver lobule in female rats but is markedly reduced in the pericentral region in male animals. By immunoelectron microscopy heme-binding protein immunoreactivity is localized in cytoplasm and nuclear matrix. The mitochondria and peroxisomes and the secretory apparatus are free of the label. In nuclei, gold labeling is confined to the interchromatin region (euchromatin) and nucleoli; condensed chromatin (heterochromatin) and nucleolus-associated chromatin are negative. The subcellular localization was substantiated by radioimmunoassay and immunoblotting of nuclear and cytosolic fractions. Immunoblotting shows that the heme-binding protein-like immunoreactive protein in the nucleus has a slightly larger molecular weight than that in the cytoplasm.

New insights into the structure and function of fatty acid-binding proteins

“…FABPs have been detected in the nucleus of hepatocytes [194,195], heart myocytes [196], locust myocytes [197] and astrocytes [198]. Recently, the role of L-FABP in FA transport to the nucleus was examined using fluoresceinconjugated L-FABP [199].…”

Ferriheme and ferroheme are isosteric inhibitors of fatty acid binding to rat liver fatty acid binding protein

“…Cytosol contains an abundant heme-binding protein (HBP) (Knobler et al 1989) localized in the cytoplasm and nucleus (Fahimi et al 1990). This protein increases the ferriheme eflux from its site of synthesis, the mitochondrion (Liem et al 1990), and can increase the partitioning of ferriheme out of a number of biological membranes (Liem et al 1994).…”

Antioxidative function of L-FABP in L-FABP stably transfected Chang liver cells

“…2,3 L-FABP is very likely to be an effective endogenous antioxidant, because it has high affinity and capacity to bind long-chain fatty acid oxidation products. 4,5 Hepatocyte L-FABP concentration could be as high as 0.4 mmol/L, 6 and it contains a large number of reducing amino acid residues (1 cysteine and 7 methionine residues) in its molecular structure.…”