Nitrogen cycle enzyme activity

Condensation of CO2, ammonia, and ATP to form carbamoyl phosphate is catalyzed by mitochondrial carbamoyl phosphate synthase I (reaction 1, Figure 29-9). A cytosolic form of this enzyme, carbamoyl phosphate synthase II, uses glutamine rather than ammonia as the nitrogen donor and functions in pyrimidine biosynthesis (see Chapter 34). Carbamoyl phosphate synthase I, the rate-hmiting enzyme of the urea cycle, is active only in the presence of its allosteric activator JV-acetylglutamate, which enhances the affinity of the synthase for ATP. Formation of carbamoyl phosphate requires 2 mol of ATP, one of which serves as a phosphate donor. Conversion of the second ATP to AMP and pyrophosphate, coupled to the hydrolysis of pyrophosphate to orthophosphate, provides the driving... 

Table 32.1 Enzyme activities relevant to marine nitrogen cycling... 

Microbial assemblage activities, including elements of the nitrogen cycle and enzyme functions, have the potential to provide information concerning the effects of chemicals on soil systems. 

Present data support the hypothesis that chitinase enzyme is inducible in estuarine sediment by natural causes, i.e., exuvial input. Biodeposit formers, such as the oyster, participate in the apparent concentration of chitinase hydrolytic activities by virtue of their feeding processes. These results suggest organism-modulated chitinase dynamics and may be useful indicators of chitin roles in the overall marine carbon and nitrogen cycles. 

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