The hypoxanthine-guanine-xanthine phosphoribosyltransferase from Tritrichomonas foetus has unique properties

Alternative IMP Binding in Feedback Inhibition of Hypoxanthine–Guanine Phosphoribosyltransferase from Thermoanaerobacter tengcongensis

“…29 But at least one PRT, T. foetus HGXPRT, seems to be active as a monomer in solution. 40 Surprisingly, this enzyme exists as a dimer in the crystal structure. 18 The fact that nearly no PRTs adopt a monomeric form raises the possibility that the formation of an oligomer has strong biological implications in facilitating the catalysis or stabilizing the special conformation of PRTs.…”

Inactivation of Tritrichomonas Foetus and Schistosoma Mansoni Purine Phosphoribosyltransferases by Arginine‐Specific Reagents

“…The dimer interface is very similar to that observed in the dimer of human HGPRT (Eads et al, 1994). This is surprising because of the previous data from gel filtration and native PAGE suggesting that the enzyme was present primarily as a monomer (Beck and Wang, 1993), whereas the mammalian enzyme exists as dimers and tetramers depending upon the ionic strength (Johnson et al, 1979). We have repeated the molecular-mass determination of native T foetus HGXPRT in the present study by FPLC gel filtration, analytical ultracentrifugation and native gel electrophoresis.…”

“…Recombinant human HGPRT was purified from the same strain of E. coli transformed with pBAcprt expression plasmid by a previously described procedure (Kanaaneh et ai., 1994). Recombinant 7: foetus HGXPRT was purified from the same strain of E. coli transformed with the pBTfprt expression plasmid (Chin and Wang, 1994) by the procedure described by Beck and Wang (1993) with minor modifications (Kanaani et al, 1996). Recombinant G. lamblia GPRT was prepared as previously described (Sommer et al, 1996).…”

“…This molecular mass did not change with changing protein concentrations or upon addition of PRibPP (1 mM) or GMP (25 pM-1 mM), suggesting that native 7: foetus HGXPRT is present primarily in the dimer form in solution, which agrees with our previous X-ray crystallographic data . A repeat of the previous experiment on gradient native PAGE (Beck and Wang, 1993) showed that, although the native dimer forms of human HGPRT (48 kDa), schistosomal HGPRT (52 kDa) and 7: foetus HGXPRT (44 kDa) differ only slightly in their molecular masses, the 7: foetus enzyme migrated faster than the other two proteins, which could be due to the unusually low PI of 4.8 for the 7: foetus enzyme (Chin, M. S. and Wang, C. C., unpublished results) compared to the PI values of 6.3, 6.16, 6.05 and 5.95 for the human enzyme (Johnson et al, 1982). This anomaly may explain the previous ei-roneous conclusion.…”

“…7: ,foetus HGXPRT shares only 27.3% sequence identity with human HGPRT (Chin and Wang, 1994) and accepts xanthine as a substrate with only a tenfold higher K,, value than that for hypoxanthine or guanine (Beck and Wang, 1993; Chin, M. S. and Wang, C. C., unpublished results). In addition, the two enzymes are different in the kinetics of their catalysed reactions.…”