(i) The metabolites affecting ATase action include 2-oxoglutarate, glutamine and A TP. 2-oxoglutarate and glutamine have antagonistic activity. When the relative concentration of 2-oxoglutarate is high, the deadenylylation activity of ATase increases, and conversion to the inactive form is inhibited. When the relative concentration of glutamine is high, the adenylylation reaction is favoured. ATP stimulates ATase to deadenylylate.
(ii) The regulatory protein (PH) that interacts with ATase is a tetramer consisting of four identical subunits (MW -11,000). PH exists in two states, the unmodified PII (PHA) and the modified PII (PIID). PIIA stimulates the adenylylation of GS by ATase. PIID is the uridylylated form of PII.
It is formed as the result of a covalent attachment of a UMP residue from UTP by the action of a uridylyltransferase (UTase). The uridylyl residue (UMP) is removed by a uridylyl removing enzyme (UR), which may be identical with UTase.
The activity of UTase is modulated by concentrations of '2-oxoglutarate and glutamine. PIID enhances the deadenylylation reaction.
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