Subcomponents C1q of the first component of guinea pig and mouse complement. Comparative study of their asparagine-linked sugar chains

Is there facilitated uptake of fatty acids by the liver? Interpretation and analysis of experimental data

Uptake of hydrophobic organic anions that are extensively bound to serum proteins has been a controversial issue for over 30 years. It is known that steady-state uptake is lower in the presence of binding proteins, but it is much higher than predicted on the basis of protein-ligand binding equilibrium. Several theories have been postulated to account for this observation. Recent work has shown how binding proteins are capable of enhancing the uptake rate of long-chain fatty acids by decreasing the diffusional resistance of the unstirred fluid layer. The enhanced transport via codiffusion is especially important for tightly bound ligands like long-chain fatty acids. Whether this model accounts for all experimental data or whether hepatocytes facilitate the uptake of protein-bound ligands, by for example mediating the protein-ligand dissociation rate, is not clear. We review the published reports to gain an understanding into the potential mechanism for the extraction of long-chain fatty acids. Understanding the uptake mechanism of these important metabolic substrates is vitally important in determining their overall utilization in a variety of clinical disorders as diverse as gallstones, obesity, and atherosclerosis.

Rat Clq: isolation and purification from normal serum and development of a sensitive hemolytic assay

Rat Clq was isolated and purified from normal rat serum by a two-step procedure: affinity chromatography on a human IgG-Sepharose 4B column and Bio-Gel A 5m column chromatography. From 1.8 l of normal serum, the procedure yielded 4.5 mg of homogeneous and hemolytically active rat Clq as shown by three bands of peptide in SDS polyacrylamide gel electrophoresis under reducing conditions and by a single precipitin line between rat Clq and rabbit anti-rat Clq antibody. Rabbit anti-rat Clq antibody prepared by immunizing a rabbit with 225 micrograms of rat Clq was specific as shown by a single precipitin line between the antibody and normal rat serum and rat Clq with complete identity. The amino acid composition of rat Clq was very similar to that of human Clq. The purification procedure also yielded Clq-depleted rat serum which was used with the homogeneous Clq to establish a sensitive hemolytic assay: 4.5-13.5 ng of rat Clq can be reproducibly quantitated. The concentration of Clq in Brown Norway rats was estimated to be 41.5 +/- 3.0 micrograms/ml serum.

A study of the role of the asparagine-linked sugar chains of human complement subcomponent C1q in its biological activities

The sialic acid residues were removed from asparagine-linked sugar chains on the C-terminal non-collagenous globular regions of human C1q by sialidase digestion. Both the haemolytic activity and the binding ability to immunoglobulin G (IgG) (Fc-binding ability) of C1q were unimpaired, even after the complete removal of sialic acid from these sugar chains. On the other hand, the rate of disappearance of C1q from the circulation was greatly accelerated by its desialylation, that is, the radioactivity of the infused intact and desialylated C1q was reduced to half for 200 min and for 140 min in the circulation of rats, respectively. A mixture of entire asparagine-linked sugar chains consisting of neutral, monosialyl and disialyl oligosaccharides was isolated from the intact C1q molecule by hydrazinolysis. The oligosaccharide-mixture isolated, after NaBH4 reduction, was added to assay system of C1q, but neither the haemolytic activity nor the Fc-binding ability was influenced.

Comparative studies on biological activities of subcomponents C1q of the first component of human, bovine, mouse and guinea-pig complement

Both the haemolytic activity and the binding ability to immunoglobulin G(IgG) (Fc-binding ability) were comparatively assayed among human, bovine, mouse and guinea-pig C1q. The haemolytic activity was measured by using the sensitized sheep erythrocytes with rabbit immunoglobulin M(IgM)- or IgG-haemolysin. The Fc-binding ability was assayed by using immune complexes made of rabbit IgG-antibody against human serum albumin as well as agglutination of latex particles coated with human, bovine or rabbit IgG (IgG-latex). The specific haemolytic activity was comparable with between bovine and mouse C1q, while those of guinea pig and human C1q were significantly lower than those of the others. Only the human and mouse C1q showed significantly positive agglutinating activity of human or bovine IgG-latex. In the case of the use of rabbit IgG-latex, each of these C1q gave much weaker agglutination. On the other hand, the ability of all these C1q to bind to Fc of immune complexes specifically was almost comparable. The discrepancy in specific activities between the haemolysis and the Fc-binding ability may suggest that these two biological activities are not always correlative and that these are independent biological phenomena.