Abstract
Adenine phosphoribosyltransferase (AMP:pyrophosphate phosphoribosyltransferase EC 2.4.2.8) which catalyzes the phosphoribosylation of cytokinin bases and adenine to form the corresponding nucleotides were partially purified from the cytosol of wheat ( Triticum aestivum) germ. This enzyme (molecular weight, 23,000 ± 500) phosphoribosylates the bases at an optimum Mg 2+ concentration of 5 m m and optimum pH of 7.5 (50 m m Tris-HCl buffer). K m values for N 6 -(Δ 2-isopentenyl)adenine, N 6 -furfuryladenine, N 6 -benzyladenine, and adenine are 130, 110, 154, and 74 μ m, respectively, in 50 m m Tris-HCl buffer (pH 7.5) at 37 °C. Hypoxanthine and guanine are not substrates for the enzyme. In concerting with other cytokinin metabolic enzymes, this enzyme may play a significant role in maintaining the supply of adequate levels of “active cytokinin.”
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