Oligosaccharide side chains of human colonic mucins contain 0-acetylated sialic acids and glycosulfate esters. Although these substituents are considered to protect the chains agiist degradation by bacterial glycosidases, sialate O-acetylesterase, N-acetylneuraminate lyase, and glycosulfatase activities have been found in fecal extracts. To better define the source of these activities, we measured extracellular and cell-bound sialidase, sialate O-acetylesterase, N-acetylneuraminate lyase, arylesterase, and glycosulfatase activities produced by 23 isolates of human fecal bacteria grown anaerobically in a hog gastric mucin culture medium; these represented dominant populations of fecal anaerobes, facultative anaerobes, and the subset of mucin oligosaccharide-degrading bacteria. Every strain produced sialidase and high levels of arylesterase, and all but five facultative anaerobes produced sialate O-acetylesterase. Sialic acids containing 2 mol or more of O-acetyl ester per mol of sialic acid were cleaved from mucin glycoproteins more slowly by sialidases of mucin oligosaccharide-degrading stains than were sialic acids containing 1 or 0 mol, and only N-acetyland mono-O-acetylated sialic acids were recovered from enzyme digests of a mucin containing di-O-acetylated sialic acids. No detectable N-acetylneuraminate lyase activity was produced by any strain, but low activity was induced by increasing the glycoprotein-bound sialic acid concentration in the culture medium of six Escherichia coli strains. Using lactitol-6-sulfate as a substrate, we found weak glycosulfatase activity in the partially purified, concentrated enzyme mixture in the culture supernatants of four mucin oligosaccharide-degrading strains but in none of the unconcentrated culture fractions. We conclude that the presence of two or more O-acetyl groups on sialic acids inhibits enteric bacterial sialidases but that production of sialate O-acetylesterases by several populations of enteric bacteria lessens the likelihood that mucin oligosaccharide chains terminating in 0-acetylated sialic acids are protected from degradation. Sialate O-acetylesterases have a role * Corresponding author.

Sialidase activity in normal faecal extracts showed a preference for mucin-related glycoprotein and oligosaccharide substrates, but the presence of two or more O-acetyl esters at positions C7-C9 on the sialic acids retarded the rate of hydrolysis. A specific sialate O-acetyl esterase was detected with a lower total activity relative to sialidase with mucin substrates and having a pH optimum of 7.8 and a KM of approximately 1 mM sialate O-acetyl ester. A specific glycosulfatase activity was found in faecal extracts using the substrate lactit-[3H]ol 6-O-sulfate with a pH optimum of pH 5.0 and a KM of approximately 1 mM. Faecal extracts from ulcerative colitis (UC) patients had higher sialate O-acetyl esterase and glycosulfatase activity, while mucin sialidase activity was unchanged. Metabolically labelled mucin isolated from UC patients contained less sulfate and had lower sialic acid O-acetylation compared with normal mucin. Colonic mucin was degraded more efficiently by faecal extracts from UC patients compared with normal extracts. The UC mucin was degraded more rapidly than the normal mucin by faecal enzyme extracts from both normal and UC subjects.

1. The activities of enzymes degrading human colonic mucin were examined in faecal specimens from healthy subjects and patients with inflammatory bowel disease. 2. The activity of sialidase was measured using a new physiological substrate related to mucus glycoproteins. In addition, acylneuraminate pyruvate-lyase (N-acetylneuraminate lyase; EC 4.1.3.3.) and a novel O-acetylsialic acid esterase (sialate O-acetylesterase; EC 3.1.1.53) were detected. 3. The O-acetylsialic acid esterase activity was readily detectable in partially purified fractions after Sephadex G-100 chromatography. 4. Patients with inflammatory bowel disease showed significant increases in acylneuraminate pyruvate-lyase and proteinase activity but sialidase activity did not differ from normal. The activity of these enzymes in neutrophils could not account for the differences observed.

1. The total sialic acid content of human gastric aspirates was measured using a colorimetric assay. Care was taken to optimize the assay and to eliminate interference. 2. The sialic acid content of gastric aspirates collected under resting conditions from 77 patients with non-ulcer dyspepsia was found to decrease with age from > 100 micrograms/ml at 25 years and younger to < 20 micrograms/ml above 70 years of age. 3. Analysis of the sialic acids by gas chromatography, mass spectrometry and thin-layer chromatography showed the presence of N-acetylneuraminic acid and two O-acylated derivatives, 9-O-acetyl- and 9-O-lactyl-N-acetylneuraminic acids. These forms were predominantly glycosidically bound. 4. Thin-layer chromatographic analysis of individual aspirate samples showed that the O-acetylated sialic acids were present in all samples, with a maximum of 25% and a minimum of 5% of the total sialic acids.

Two mucins were isolated from bovine submandibular glands and termed major and minor on a quantitative basis. The major mucin representing over 80% of the total glycoprotein fraction contained 37% of its dry weight as protein in contrast to 62% for the minor mucin. Differences in the amino acid composition reflected the higher proportion of typically non-glycosylated peptide in the minor mucin. The molar ratio of N-acetylgalactosamine to serine plus threonine was 0.82 in major and 0.65 in minor mucins, indicating a lower degree of substitution of potential glycosylation sites in the minor mucin. Differences in the carbohydrate composition were found largely related to the sialic acids, with higher relative amounts of N-glycoloylneuraminic acid in the minor mucin. In addition, the proportion of di-O-acetylated sialic acids was higher in the major mucin. The rate of sialidase action on the two mucins could be correlated with the content of N-glycoloylneuraminic acid in each glycoprotein. There was no difference in the type of oligosaccharide found in each mucin and the differences in relative proportions reflected the monosaccharide composition for the two mucins. Gel filtration on Sepharose CL 2B showed a lower molecular weight distribution for the minor in contrast to the major mucin which was partially excluded. Density gradient centrifugation reflected this variation. SDS-PAGE demonstrated a regular banding pattern for the major mucin with a lowest subunit size of 1.8 x 10(5) Da and aggregates in excess of 10(6) Da, while the minor mucin ranged from 3.0 x 10(5) to 10(6) Da. The chemical composition of the isolated mucins was compared with previous histochemical analysis of mucin distribution in bovine submandibular glands and indicates a possible cellular location for each mucin.