Epoxy compounds usually have stronger nucleophilic ability, because the alkyl group on the oxygen atom makes the bond angle smaller, which makes the lone pair of electrons react more dissimilarly with the electron-deficient system. Compound: 2-Amino-6-methylpyrimidine-4-thiol, is researched, Molecular C5H7N3S, CAS is 6307-44-4, about Guanine phosphoribosyltransferase from Escherichia coli. Specificity and properties.Related Products of 6307-44-4.
The specificity and properties of a novel guanine phosphoribosyltransferase of E. coli were studied and compared to those of the hypoxanthine-guanine phosphoribosyltransferase from other sources. The structural requirements for binding of purines to this enzyme were explored by the determination of the Ki values for 100 purines and purine analogs. The most effective binding occurred when the purine contained an oxo or SH group in the 6 position and an NH2 or OH group in the 2 position. Unlike the hypoxanthine-guanine phosphoribosyltransferase from other sources, this enzyme bound hypoxanthine 67 times less effectively than guanine and 4 times less effectively than xanthine. Rates of nucleotide formation from a number of purines and purine analogs were also determined The enzyme had a pH optimum from 7.4 to 8.2. From secondary double-reciprocal plots derived from an initial velocity anal., the Km values were 0.037mM for guanine and 0.33mM for 5-phosphoribosyl 1-pyrophosphate. The enzyme was sensitive to inhibition by p-chloromercuribenzoate, and this inhibition could be reversed by either dithiothreitol or β-mercaptoethanol. The apparent activation energy with guanine as substrate was 12,800 cal/mole below 23° and 3370 cal/mole above 23°. Using isoelec. focusing, the guanine phosphoribosyltransferase had an apparent pI of 5.50, while the pI of a 2nd enzyme which was specific for hypoxanthine was 4.8.
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