Encapsulation of protein in humic acid from a histosol as an explanation for the occurrence of organic nitrogen in soil and sediment

Recent work suggests that nitrogen in humic acids exists primarily as amide functional groups that mirror those in protein. However, the mode for the existence of such labile materials as protein still remains unclear. With t he combined applications of NMR spectroscopy, tetramethylammonium hydroxide (TMAH) thermochemolysis, pyrolysis/GC/MS, and elemental analysis, we propo se that the survival of proteins in humic acids is carried out by encapsula tion into hydrophobic domains of humic acids. To test this hypothesis, we s imulated encapsulation of N-15-labeled protein extracts into humic acids an d demonstrated that complete hydrolysis of the protein is prevented by the encapsulating humic acid. Results from this study constitute evidence to su pport the encapsulation mechanism involved in the formation of refractory o rganic nitrogen during sediment diagenesis. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.