ABSTRACT
The number and distribution of galactose-specific binding sites were investigated in rat liver cells during perinatal development. Ligand binding to hepatocytes, macrophages and endothelial cells was followed with in vitro and in situ experiments by electron microscopy, using lactosylated bovine serum albumin adsorbed onto 5 nm colloidal gold particles as ligand. Binding capacity, starting at a late stage of fetal development, is very low both on the hepatocyte and on the macrophage surface, which show single particles statistically distributed. By contrast, bound particles are absent from fetal endothelial cells, which also lack the typical coated regions. In vivo, experiments at 37 degrees C show that endocytosis occurs to some extent in prenatal life. These results indicate that the expression of galactose-specific receptors' activity on the different liver cell types follows different developmental patterns, which are independently modulated.
Subject(s)
Liver/embryology , Receptors, Cell Surface/analysis , Animals , Animals, Newborn/metabolism , Liver/growth & development , Liver/metabolism , Macrophages/metabolism , Male , Microscopy, Electron , Rats , Rats, Inbred Strains , Rosette FormationABSTRACT
Acid hydrolysis of trichloroacetic acid precipitate from rat tissue (liver, kidney and testis) homogenate released significant amounts of acid-insoluble putrescine, spermidine and spermine. Following incubation of liver homogenate with [1,4-14C]putrescine, 1.4% of total radioactivity and 1.0% of labelled diamine were recovered in the acid-insoluble fraction. Exhaustive digestion of acid-precipitable material with proteinases (Pronase, aminopeptidase M, carboxypeptidase A, B and Y) revealed the presence of di- and polyamines and of N1-(gamma-glutamyl)spermidine, N1-(gamma-glutamyl)spermine and N1,N12-bis(gamma-glutamyl)spermine. These derivatives were identified both by chromatographic analysis and by enzymatic digestion with purified gamma-glutamylamine cyclotransferase. The finding of di- and polyamine gamma-glutamyl derivatives in the proteinase-digested acid-insoluble fraction of homogenate may be considered as a proof of the in vivo transglutaminase-catalyzed binding of polyamines to proteins. This evidence suggests that di- and polyamines might have an important role in mammalian tissues through covalent binding to proteins by either one or both the primary amino groups.
Subject(s)
Liver/analysis , Polyamines/metabolism , Protein Processing, Post-Translational , Proteins/metabolism , Animals , Chromatography, Ion Exchange , Glutamine/metabolism , Kidney/metabolism , Male , Peptide Hydrolases/metabolism , Putrescine/metabolism , Rats , Rats, Inbred Strains , Spermidine/metabolism , Spermine/metabolism , Testis/metabolism , gamma-Glutamylcyclotransferase/metabolismABSTRACT
The ontogeny of asialoglycoprotein receptor was investigated by electron microscopic cytochemistry in hepatocytes isolated from foetal and adult rat. The binding capacity for asialofetuin coupled to horseradish peroxidase was lacking before the 18th day of intrauterine life; it arises at this time and increases with developmental age. The ligand-receptor complexes form small patches. The distribution pattern of positivity is very similar in pre and postnatal age, covering the entire cell surface. These results indicate a rather late appearance of the galactose-binding capacity related to the asialoglycoprotein clearance function, which is typical of adult mammalian liver.
