Adenylyl Sulfate Reductases EC

Two major pathways are known for the reduction of sulfate. One is the assimilatory pathway, which reduces sulfate to the extent necessary for satisfying the nutritional requirements of the organism. In this pathway, which has been extensively studied in yeast by Robbins and Lip-mann (S68) and Bandurski and his colleagues 369, 370), sulfate is first activated in the presence of ATP by the enzyme ATP-sulfurylase to form adenosine 5 -phosphosulfate (APS). Then in a second reaction, APS is phosphorylated in the 3 position by ATP to form 3 -phosphoadenosine 5 -phosphosulfate (PAPS) 

The second pathway by which sulfate is reduced is the dissimilatory pathway in which sulfate is the terminal electron acceptor and leads to the formation of large quantities of H2S. During the dissimilatory reduction of sulfate, APS is formed as in Eq. (6). Then APS is reduced directly to sulfite and AMP by the enzyme APS-reductase. Table XVIII shows the data of Peck 373) on the pathway of sulfate reduction in various microorganisms. 

Adenylyl sulfate (APS) reductase is a flavoprotein, which contains iron and possibly acid-labile sulfide. It catalyzes the reduction of APS in the 

Pathway of Sulfate Reduction in Various Types of Microorganisms  

It can also catalyze the reverse reaction when ferricyanide or cytochrome c is used as electron acceptor (374, 375). The phosphosulfate bond of 

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