Abstract
This chapter discusses the sulfate-activating enzymes. The two sulfate-activating enzymes, ATP-sulfurylase (ATP:sulfate adenylyltransferase; sulfate adenylyltransferase), and APS kinase (ATP: adenylylsuifate 3'-phosphotransferase; adenylylsulfate kinase), catalyze the activation of inorganic sulfate first to APS (adenosine- 5'-phosphosuifate or 5'-adenylylsulfate) and then to PAPS (adenosine Y-phosphate 5'-phosphosulfate, or 3'-phospho-5'-adenylylsulfate, or 3'-phosphoadenosine 5'-phosphosulfate). Although the equilibrium of the sulfurylase reaction lies far to the left, the overall production of PAPS in vivo is promoted by the hydrolysis of the inorganic pyrophosphate, and the favorable APS kinase reaction. The chapter presents the assay methods for ATP – sulfurylase such as colorimetric molybdolysis (Pi formation) assay; continuous spectrophotometric molybdolysis (AMP release) assay; and continuous spectrophotometric (APS Kinase-Coupled) assay. Assay methods for APS kinase are also described. If homogeneous sulfate-activating enzymes are unavailable, substrate amounts of unlabeled PAPS can be prepared using partially purified fractions from yeast, rat liver, chlorella, chick embryo chondrocytes, or P. chrysogenum, or can be prepared by organic synthesis.
Published Version
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