Amidophosphoribosyltransferase

Amidophosphoribosyltransferase (ATase) is an enzyme that plays a crucial role in the de novo synthesis of purine nucleotides. It catalyzes the first committed step in the purine biosynthetic pathway, which is the conversion of phosphoribosyl pyrophosphate (PRPP) to 5-phosphoribosylamine (PRA).

Function

Amidophosphoribosyltransferase is responsible for the amination of PRPP, a reaction that involves the transfer of an amide group from glutamine to PRPP, forming PRA. This reaction is essential for the production of inosine monophosphate (IMP), a precursor for both adenine and guanine nucleotides.

Structure

The enzyme is a homotetramer composed of four identical subunits. Each subunit contains an active site where the substrate binding and catalysis occur. The enzyme requires magnesium ions as cofactors for its activity.

Regulation

The activity of amidophosphoribosyltransferase is tightly regulated by feedback inhibition. High levels of adenosine monophosphate (AMP) and guanosine monophosphate (GMP) inhibit the enzyme, ensuring a balanced supply of purine nucleotides within the cell.

Clinical Significance

Mutations in the gene encoding amidophosphoribosyltransferase can lead to disorders in purine metabolism. One such disorder is phosphoribosylpyrophosphate synthetase superactivity, which can result in excessive purine production and associated conditions such as gout.

See Also

• Purine metabolism
• Phosphoribosyl pyrophosphate
• Inosine monophosphate
• Gout