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Sulfuryl transfer catalyzed by phosphokinases
1Department of Chemistry, University of Wisconsin, Madison 53706.
Biochemistry
|January 29, 1991
Summary
Adenosine 5'-sulfatopyrophosphate acts as a substrate for nucleoside diphosphate kinase, undergoing sulfuryl transfer via a ping-pong mechanism. This reaction lacks a strict divalent metal requirement and is slower than phosphoryl transfer, suggesting a distinct catalytic role for metal ions.
Area of Science:
- Biochemistry
- Enzymology
- Chemical Biology
Background:
- Nucleoside diphosphate kinase (NDK) is a key enzyme in cellular metabolism.
- NDK typically catalyzes the transfer of a phosphoryl group from nucleoside triphosphates to nucleoside diphosphates.
- Adenosine 5 '-sulfatopyrophosphate (AppSO4) is a structural analog of ATP.
Purpose of the Study:
- To investigate the substrate specificity of NDK using AppSO4.
- To elucidate the mechanism of sulfuryl transfer catalyzed by NDK.
- To compare sulfuryl transfer with the known phosphoryl transfer reactions.
Main Methods:
- Enzymatic assays using AppSO4 as a substrate.
- Kinetic analysis of NDK-catalyzed reactions.
- Comparison of metal-dependent and metal-independent reaction rates.
Main Results:
- AppSO4 is a substrate for NDK, with sulfuryl transfer occurring via a ping-pong mechanism.
- Sulfuryl transfer reactions do not require divalent metal ions, unlike phosphoryl transfers.
- Metal- and nonmetal-catalyzed sulfuryl transfer rates differ minimally and are significantly slower than phosphoryl transfers.
- Metal ions likely coordinate the phosphate groups of the substrate.
Conclusions:
- NDK can catalyze sulfuryl transfer reactions in addition to phosphoryl transfer.
- The absence of a strict metal requirement for sulfuryl transfer suggests a different catalytic role for metal ions in NDK.
- Both sulfuryl and phosphoryl transfers likely proceed through dissociative transition states.