BIOL 195 |
| Hint1 and Fhit are members of the HIT superfamily tumor suppressors. Nevertheless, Fhit is an Ap3A hydrolase and purine nucleoside phosphoramidase, while Hint1 possesses only phosphoramidase activity. Both Fhit and Hint1 exist as homodimers with a large flat monomer-monomer interface. Unlike Fhit, the C-terminal residues of each Hint monomer are in close proximity to the catalytic residues in the active site of the other monomer. After replacement of the centrally located interface residue, Val-97, with either Asp, Glu, or Arg, only monomeric structurally similar protein was observed by SEC and CD analysis, For the Val-97 to Asp mutant, steady-state kinetic analysis with a new highly sensitive continuous assay, revealed a modest 4- fold reduction in the kcat value relative to wild-type, while the value of Km was increased by 200-fold, thus resulting in a 1000–fold reduction in kcat/Km. Therefore, Hint1 homodimerization appears to largely govern substrate binding, but not the rate of catalysis. |
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Enzymes
4:30 PM-6:30 PM, Wednesday, 13 September 2006 Moscone Center -- Hall D, Poster
Sci-Mix
Division of Biological Chemistry |