Studies on the interaction of concanavalin A with glycoproteins

Lectins (phytohaemagglutinin) are known to have the unique property of binding with certain specific sugars, polysaccharides and glycoproteins. Although the kinetics of interaction between lectins and sugar have been extensively studied, the binding characteristics of the lectins with various glycoproteins are not well understood. In this laboratory a systematic study has been initiated in relation to the interaction of lectins with glycoproteins. Concanavalin A is known to bind alpha-glucosides, mannosides and biopolymers having these sugar configurations. A galactose binding protein from caster bean has been purified to homogeneity and was found to contain mannose. This lectin was used as the source of glycoprotein for studying its interaction with concanavalin A. This study showed that the interaction is temperature dependent and the dissociation is time and alpha-methyl glucoside concentration dependent. This has led to speculate a model for cell-lectin interaction. Using concanavalin A it has been shown that all the lysosomal enzymes from brain studied were glycoprotein in nature. Moreover, using Sepharose-bound concanavalin A it has been possible to devise a method by which these lysosomal enzymes could be purified considerably. With the knowledge that the interaction between lectin and glycoprotein is not only dependent on the specific sugar present in the glycoprotein, but also on the nature of the glycoprotein it was possible to develop a novel method for immobilizing various glycoprotein enzymes, such as arylsulphatase A, hyaluronidase and glucose oxidase.

Acylation of lysolecithin in the intestinal mucosa of rats

1. The presence of an active acyl-CoA–lysolecithin (1-acylglycerophosphorylcholine) acyltransferase was demonstrated in rat intestinal mucosa. 2. ATP and CoA were necessary for the incorporation of free [1-14C]oleic acid into lecithin (phosphatidylcholine). 3. The reaction was about 20 times as fast with [1-14C]oleoyl-CoA as with free oleic acid, CoA and ATP. 4. With 1-acylglycerophosphorylcholine as the acceptor, both oleic acid and palmitic acid were incorporated into the β-position of lecithin; the incorporation of palmitic acid was 60% of that of oleic acid. 5. Of the various analogues of lysolecithin tested as acyl acceptors from [1-14C]oleoyl CoA, a lysolecithin with a long-chain fatty acid at the 1-position was most efficient. 6. The enzyme was mostly present in the brush-border-free particulate fraction of the intestinal mucosa. 7. Of the various tissues of rats tested for the activity, intestinal mucosa was found to be the most active, with testes, liver, kidneys and spleen following it in decreasing order.

Biochemical Effects of the Porphyrinogenic Drug Allyisopropylacetamide

Successive administrations of allylisopropylacetamide, a potent porphyrinogenic drug, increase liver weight, microsomal protein and phospholipid contents. There is an increase in the rate of microsomal protein synthesis in vivo and in vitro. The drug decreases microsomal ribonuclease activity and increases NADPH-cytochrome c reductase activity. Phenobarbital, which has been reported to exhibit all these changes mentioned, is a weaker inducer of delta-aminolaevulinate synthetase and increases the rate of haem synthesis only after a considerable time-lag in fed female rats, when compared with the effects observed with allylisopropylacetamide. Again, phenobarbital does not share the property of allylisopropylacetamide in causing an initial decrease in cytochrome P-450 content. Haematin does not counteract most of the biochemical effects caused by allylisopropylacetamide, although it is quite effective in the case of phenobarbital. Haematin does not inhibit the uptake of [2-(14)C]allylisopropylacetamide by any of the liver subcellular fractions.