Diguanosinetetraphosphate guanylohydrolase in Artemia salina

Abstract

1. The diguanosinetetraphosphate guanylohydrolase (EC 3.6.1.17) of Artemia salina has been found to be located in the cytosol while its substrate, diguanosine tetraphosphate, is in the sediment. 2. Two spectrophotometric methods have been developed to study this enzyme. One is based in the evaluation of one of the products, GTP, coupled to the auxiliary enzymes phosphoglycerate kinase/glyceraldehyde-3-phosphate dehydrogenase. The other method is based on the hyperchromicity observed at 252 nm by the splitting of diguanosine tetraphosphate. 3. With a partially purified preparation, the following enzymatic properties have been found: for diguanosine tetraphosphate, 5 μM. GMP, GDP, GTP and ATP were competitive inhibitors of the reaction with values of 24, 56, 14 and 30 μM respectively. 4. Even lower values were obtained with the guanosine 5′-tetraphosphate and adenosine 5′-tetraphosphate, which were 0.006 and 0.13 μM, respectively. These rather low values suggest a possible role for these compounds as metabolic regulators.