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Stabilization of Amino Sugar Units in Humic-Type Polymers¹

ABSTRACT

Studies were conducted on the stabilization of amino sugar compounds against microbial degradation by the nucleophilic addition of the amino group to the aromatic nuclei of quinones. In accord with previous respirometer studies with amino acids and peptides, the presence of glucosamine or chitosan (polyglucosamine) increased O₂ uptake in reaction mixtures of phenolics undergoing enzymatic or autoxidative polymerization. Model humic acids were prepared by enzymatic or autoxidative polymerization of mixtures of phenols commonly found to occur in soil or fungal humic acids. Labeled ¹⁴C glucosamine and chitosan were incorporated separately into these model polymers and the stabilization of the carbohydrate C against microbial attack in soil studied. For comparative purposes, peptone was also incorporated into model polymers. During a 12-week soil incubation period 15–23% of the ¹⁴C activity of the glucosamine model polymers was evolved as CO₂, whereas over 70% was evolved when glucosamine was added to the soil alone or mixed with a preformed model polymer. Four to 11% of the polymers incorporating peptone decomposed during this period. During an 8-week period, 53% of the chitosan was lost as CO₂ when added alone but only 31% of the chitosan which had been incorporated into the model humic polymer was lost. From 5–15% of the ¹⁴C activity in the glucosamine-phenol model polymers could be solubilized by a 24 hour, 100C, 6N HCl hydrolysis. Residual ¹⁴C activity was distributed among all soil humus fractions after the incubation period. Infrared spectra were obtained of the model polymers alone, and incorporating glucosamine and peptone. Significant changes in absorbance occurred depending on the functional groups incorporated.

¹ Contribution from the Dep. of Soil Sci. and Agr. Eng., Univ. of California, Riverside 92501, and Institut für Biochemie des Bodens, Forschungsanstalt für Landwirtschaft, Braunschweig, Germany.

² Research Assistant and Professor of Soil Science, respectively, Dep. of Soil Sci. and Agr. Eng., Univ. of California, Riverside, and Biochemist, Institut für Biochemie des Bodens, Forschungsanstalt für Landwirtschaft, Braunschweig, Germany. The authors wish to thank Dr. S. Bartnicki-Garcia, Dep. of Plant Pathology, Univ. of California, Riverside, for supplying the culture of Mucor rouxii and helpful suggestions.

Received for publication January 26, 1972. Accepted for publication March 8, 1972.