Enzyme Activities in Aquatic Systems

Several general approaches have been used to measure the activities of extracellular enzymes in aquatic systems. These methods typically measure a potential activity, inasmuch as a substrate added to a sample to measure enzyme activity is in competition with naturally occurring substrates (whose concentration is usually unknown) for enzyme active sites. The most commonly applied method involves a small substrate proxy, typically consisting of a monosaccharide or an amino acid covalently linked to a small fluorophore substrates frequently used include methyumbellifery- (MUF-) monosaccharides and 4-methyl-coumainylamide (MCA)- amino acids. Upon hydrolysis of the bond between the monomer and the fluorophore, the fluorophore becomes fluorescent, and hydrolysis is measured as an increase in fluorescence signal with time (Hoppe, 1983 Somville and Billen, 1983). 

High-molecular-weight solid substrates such as hide powder azure, and cellulose, chitin, and agar stained with remazol brilliant blue R have been used in enzyme assays to investigate activities in extracts from sediments (Reichardt, 1986). This technique is one of the few means of examining the particle — dissolved transition in relationship to sedimentary enzyme activity, but the necessity of extracting enzymes from sediments complicates interpretation of the results, because extraction efficiency, as well as the 

EXTRACELLULAR ENZYME ACTIVITIES IN THE WATER COLUMN AND SEDIMENT 

Relative enzyme activities associated with particles and with free-living bacterial communities are not constant, however. Particle composition and concentration, as well as the attached microbial community and its associated enzyme activities, can change dramatically as a result of biological and physical processes. For example, Middelboe et al. (1995) found that as a 

In spite of these caveats, studies of enzyme activities in sediments show some recurring features. Seasonal cycles in primary productivity in temperate 

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