The Role of Protein as a Contributor to Organic Nitrogen in the Ocean

University Of Maryland Center For Environmental Sciences, Cambridge MD

Investigators

Abstract

ABSTRACT OCE-0352041 The importance of the large refractory organic nitrogen pool in the overall nitrogen cycle is well recognized, but its chemical composition and the mechanism(s) responsible for its resistance remain unanswered. Recent work has documented the importance of the amide linkage to organic nitrogen preserved in sediments and soils. The principal investigator on this project and others at the Chesapeake Biological Laboratory have recently shown that proteins can be preserved during early diagenesis and extracted from sediments. The overriding premise of this proposal is that those proteins that are preserved might retain the signal of their original biosynthesis, with only minor modification to their structure. If this is true, then structural identification of individual proteins and mixtures can be used to detail the origins of such proteins and the likely processing which allow their eventual incorporation into sediments. There are therefore two objectives of this project: To adapt current mass spectrometric methods for the analysis of primary protein structure to determine the origin and contributions of proteins and their modified products in detrital material and sediments. The primary sequence of amino acids and secondary protein structure will allow not only the major inputs to be assessed, but also the possible contribution of bacterial carbon and nitrogen to the undefined organic pool. Using a combination of field collections and experimental incubations, to determine if subtle structural modifications to proteins can help account for the missing sink of organic nitrogen that is not quantified as total hydrolysable amino acids or extractable proteins. Modified protein might represent an important fraction of organic nitrogen, but is either not available to microbial attack or exists as an end product of the degradative process. Subtle alterations to protein structure may be another important piece of the puzzle in understanding the preservation and long-term sequestration of organic nitrogen (and carbon) in marine systems.