Studies of the limited degradation of mucus glycoproteins. The effect of dilute hydrogen peroxide

Abstract

1. The action of dilute H2O2 on a series of ovarian-cyst glycoproteins and glycopolypeptides was investigated. 2. Both native glycoproteins and the glycopolypeptides were carbohydrate-rich, of relatively low molecular weight and of simple structure. 3. At pH 5.6 and 37 degrees C, exposure to H2O2 for a limited time brought about a partial degradation, the molecular weight being decreased by 2-4-fold. 4. Carbohydrate analysis showed very little change in the oligosaccharide moiety, apart from a small decrease in sialic acid in some samples. 5. Amino acid analysis showed minor changes in serine, threonine and proline contents, but almost total loss of histidine. Concomitantly, there was a small gain in aspartic acid. 6. Myosin, examined at both pH 5.7 and 6.7, exhibited generally similar behaviour, there being losses of other amino acid residues as well as histidine: the viscosity was decreased to a low value, and a range of peptides of widely varying size was produced. 7. It is suggested that attack on the histidine residue, with partial conversion into aspartic acid, is accompanied by scission of the histidyl peptide bond.

Interactions of oxygen radicals with airway epithelium.

“…The sugar moieties in mucus may act similarly to mannitol and glucose in scavenging hydroxyl radical and H202 (45,46). Mucus glycoproteins react with H202; in the process both H202 and glycoproteins are degraded (44,47,48 (52), increased nonspecific airway reactivity, increased specific airway resistance, increased respiratory frequency on exercise, and an involuntary reduction of maximal inspiratory capacity (53). It should be noted that 03 decreases mucociliary transport in sheep (54) and other species in contrast to the human data mentioned above.…”

Role of Nitric Oxide and Mucus in Ischemia/Reperfusion-Induced Gastric Mucosal Injury in Rats

“…This proposal is based on the fact that certain sugars such as glucose or mannitol are potent hydroxyl radical scavengers, and mucus contains very high concentrations of some similar sugars (Nacetylglucosamine, galactose and fucose). Conversely, the mucus gel cover of the gastric mucosal surfaces was degraded to fragments, while viscosity and gel-forming properties were reduced after reaction with hydroxyl radicals and hydrogen peroxides [41,42]. It was reported that this fragmentation with a decrease in the viscosity of gastric mucus accompanied by an increase in its thiobarbituric acid reactivity is indicative of oxidative damage to the tissues [43].…”

Chemical alteration by tooth bleaching of human salivary proteins that infiltrated subsurface enamel lesions —Experimental study with bovine lesion model systems—

“…H2O2 has been reported to severely fragment proteins such as myosin, but not lysozyme. Conversions of histidine into aspartic acid, as well as the loss of methionine, tyrosine, cysteine, and proline, may be involved in the cleavage of peptide bonds 33,34) . Statherin, which contains 62 residues, is rich in proline (7 residues) and methionine (3 residues) 35) and may be degraded into small fragments, as is myosin 33) .…”

“…Conversions of histidine into aspartic acid, as well as the loss of methionine, tyrosine, cysteine, and proline, may be involved in the cleavage of peptide bonds 33,34) . Statherin, which contains 62 residues, is rich in proline (7 residues) and methionine (3 residues) 35) and may be degraded into small fragments, as is myosin 33) . Indeed the in-office bleaching agent we used, whose active ingredient is a high concentration of H 2O2, was shown to be effective for bleaching 36) .…”