Rat colonic mucosal cell sialic acid metabolism in azoxymethane-induced tumours.

Colonic tissue was examined from normal (control) rats and azoxymethane- (carcinogen-) treated animals. Tumour-bearing colons from azoxymethane-treated rats were divided into malignant and non-malignant areas. Mucosal cells were prepared from the three types of colonic tissue and then examined for DNA and protein content and for the activities of ten enzymes involved in sialic acid metabolism. Enzyme activities were related to either the protein or the DNA content of fractions. The DNA content of cell homogenates was significantly different between tumour and non-malignant tissue and between both these tissues and normal mucosa. The protein content of the 100000 X g membrane pellet and supernatant fraction did not vary significantly between normal and non-malignant material but both these tissues differed significantly from tumour tissue. Significant variation between normal control and tumour tissue was detected at all levels of sialic acid metabolism, including N-acetylhexosamine interconversion and phosphorylation, sialic acid formation and activation, CMP-NeuAc breakdown and transfer and sialic acid release from glycoconjugates. The results indicate that major changes at all levels of sialic acid metabolism are associated with malignancy in rat colonic mucosa. Some of these changes are apparent in non-malignant mucosa and may reflect a pre-malignant state.

C-reactive protein and serum amyloid P component in the plaice (Pleuronectes platessa L.), a marine teleost, are homologous with their human counterparts.

C-reactive protein and serum amyloid P component were isolated from serum of the plaice (Pleuronectes platessa L.), a murine teleost. The isolation was based on their calcium-dependent binding affinity for pneumococcal C-polysaccharide and for agarose, respectively. These specificities are the same as those of human C-reactive protein and serum amyloid P component, respectively, and we have previously reported that the plaice molecules resemble human C-reactive protein and serum amyloid P component in their electron microscopic appearance. We describe here estimation of the molecular weights of plaice C-reactive protein and serum amyloid P component and their subunits, and analysis of their amino acid composition, glycosylation and partial amino-terminal amino acid sequences. The results establish that plaice C-reactive protein and serum amyloid P component are homologous with each other and with their human counterparts and indicate that there has been stable conservation of this protein family throughout vertebrate evolution.

The glycoconjugate content of human faeces and ileostomy effluents.

Normal human faeces and effluent from terminal ileostomies in patients with ulcerative colitis were collected. The results for ileostomy effluent given as g/24 h (mean +/- SD; n = 12) were as follows: wet weight, 897 +/- 120; total dry weight, 84 +/- 8; non-diffusible dry weight 46 +/- 5. The corresponding results for faeces (n = 6) were 104 +/- 24; 26 +/- 6; 19 +/- 5. Whereas approximately 15% of the total dry weight of ileostomy effluent appeared to consist of mucin-derived material, only trace amounts of such material could be detected in faeces.

Some aspects of the glycoprotein and glycopolypeptide content of human gastric mucus.

The carbohydrate content of non-diffusable, glycoprotein and glycopolypeptide material has been studied in normal human gastric aspirates. Pentagastrin doubles the volume of secretions but has no effect on the amount of non-diffusable material. Only about 40% of the weight of the non-diffusable material is mucin in nature. Gel-permeation chromatography indicated that about half of the mucin survived as high molecular mass glycoprotein. Monosaccharide differences, for example between secretors and non-secretors, only became manifest at the glycopolypeptide stage. These results emphasize the dangers of attempting to assess mucin changes by simple carbohydrate analyses of unfractionated gastric aspirates.

The nature of gastric secretions in a patient with Zollinger-Ellison syndrome without peptic ulceration.

A study has been made of the gastric secretions from a patient with Zollinger-Ellison syndrome without peptic ulceration, before and after treatment with cimetidine. The amount of non-diffusable glycoconjugates was measured as an index of mucin output, and found to be within normal limits. Cimetidine, which greatly reduced the volume of secretions, had no effect on the non-diffusable glycoconjugates. These results may explain the absence of peptic ulceration in certain patients with this syndrome.

The glycoprotein content of meconium.

Meconium pooled according to blood group activity has been studied. It was found to consists largely of glycoproteins. Two glycoprotein fractions have been isolated, one of which consisted of mucous-type glycoproteins and the other of "mannose-containing" glycoproteins.

A comparison of the results of sequential hydrazinolysis-nitrosation and alkali-mediated cleavage-nitrosation of the O-linked oligosaccharides of gastric mucus glycoproteins.

Analysis of the oligosaccharides released from pig gastric mucus glycopolypeptides by hydrazinolysis showed that degradation had occurred. Nitrosation of the products followed by reduction gave a mixture that had a low content of 2,5-anhydro-D-talitol, which implied destruction of much of the terminal reducing 2-amino-2-deoxy-D-galactose. Under the conditions of hydrazinolysis, cellobiose was largely unchanged but laminaribiose gave a complex mixture that probably contained glucose hydrazone (13C-n.m.r. data). In order to avoid degradation, the hydrazinolysis-nitrosation sequence should be applied to the reduced oligosaccharides released on cleavage with alkali.

The gastric mucosal barrier.

The gastric mucosal barrier is a complex system made up of submucosal, epithelial and mucus elements. The mucus gel layer is a thick tenacious organized layer adherent to the epithelium. Despite these properties it is composed of more than 95% water, the organization being provided by long interacting glycoprotein molecules (mucus glycoprotein or mucin). These molecules are largely made up of carbohydrate which is present in large numbers of relatively small oligosaccharide units packed around the polypeptide core. This structure provides clues to the nature of the protection afforded by the mucus layer. For example, it is relatively resistant to proteolysis in the gastrointestinal tract; it retains water in an unstirred layer; the tangled glycoproteins exclude large molecules and the carbohydrate of the oligosaccharide units mirror that at the surface of the epithelial cell. Few biochemical studies have been carried out on the effect of ulcer-healing drugs on gastric mucus. Normal subjects were, therefore, given two weeks treatment with cimetidine, carbenoxolone or misoprostol and the secretions aspirated from the unstimulated and pentagastrin-stimulated stomach. The volume of secretion and weight and carbohydrate content of non-diffusable glycoconjugates were determined for each specimen, together with the proportion of high molecular mass mucin and qualitative and quantitative analyses of the glycopolypeptide. There were no significant differences between the results for each drug or without drug. This may be because normal subjects were studied who already have an effective mucosal barrier. In addition, it is likely that the process of mucus biosynthesis and secretion in a healthy individual is relatively resistant to the action of ulcer healing drugs.

Measurement of sialyl-transferase activity in isolated colonic mucosal cells of the rat.

An assay for sialyl-transferase activity in isolated rat colonic mucosal cells has been developed. Total and specific activity with asialobovine sub-mandibular gland glycoprotein and endogenous substrates was approximately two-fold higher in the proximal, relative to the distal, colon. These activities were similar when asialo-alpha-acid glycoprotein was used as substrate. Endogenous activity was approximately 10-fold lower than with exogenous substrates in both proximal and distal colonic segments. Analysis of total and specific sialyl-transferase activity up to 7 weeks after jejunoileal bypass (JIB) and sham operation showed a marked increase at the first week, decreasing toward normal by week 7. Similar differences between proximal and distal colon, and with the type of substrate, were found with both groups of operated animals. Histochemical analysis showed small elevation after 1 week for sialo and sulphomucins after the JIB operation only.