ABIOTIC TRANSFORMATION OF LABILE PROTEIN TO REFRACTORY PROTEIN IN SEA-WATER

In order to determine if organic matter dissolved in sea water may undergo abiotic alterations that make it resistant to microbial degradation, the protein ribulose 1,5-bisphosphate carboxylase (RuBPcase) was abiotically aged in sterile sea water and then exposed to natural bacterial assemblages. Rates of protein assimilation decreased when protein was aged as little as 6 h; protein aged for 40 days was degraded 4-fold more slowly than non-aged protein. Abiotic modification rates, calculated from decreases in degradation rate with increasing aging time, were highest during the initial day of aging (0.8-4.8 d-1) and then decreased to 0.03 d-1. No aging effect was observed in organic-free sea water, indicating that organic-organic interactions produced the refractory protein. Amino acids from the protein were fully recovered after acid hydrolysis, indicating that the decreased lability was not caused by acid-stable molecular changes to the protein. Abiotic complexation of labile organic compounds with existing DOM may be a critical first step in the formation of refractory organic materials.