AMINO-ACID-COMPOSITION OF PEPTIDES PRESENT IN ORGANIC-MATTER FRACTIONS OF SANDY LOAM SOILS

Organic matter was extracted from cultivated and uncultivated portions of two sandy loam soils using a mild pretreatment and chelation procedure. Soil organic constituents were separated into various molecular weight fractions by gel permeation chromatography. Molecular weight fractions were analyzed for peptide content using reverse-phase high performance liquid chromatography; isolated peptide fractions were acid hydrolyzed and analyzed in this manner for their amino acid content. Peptide amino acid composition of corresponding size fractions often differed between uncultivated and cultivated soils of the same series, but cultivation did not consistently influence the content or composition of soil peptides in molecular weight fractions. The contributions of peptide amino acid N to the total N pool of Queens sandy loam were 16.01% and 3.82% for the cultivated and uncultivated soil, respectively. The contributions of peptide amino acid N to the total N pool of a Pugwash sandy loam were 2.38% and 7.55% for the cultivated and uncultivated soil, respectively. Fifteen different amino acids were recovered from hydrolyzed peptides of the Queens soil whereas 16 different amino acids were recovered from the Pugwash soil. Some amino acids, notably serine and glycine, were more common in Queens than in Pugwash peptide fractions.