Anomeric specificity of phosphofructokinase from rabbit muscle

Rabbit muscle phosphofructokinase apparently utilizes only the β furanose anomer as disclosed by rapid quench kinetic studies employing D fructose 6 P and D tagatose 6 P. Approximately 80% of the substrate, a figure that closely corresponds to the percentage β anomer, is converted to the diphosphate in a rapid initial phase. Investigations utilizing methyl α,β D fructofuranoside 6 P as a substrate analog demonstrated exclusive phosphorylation of the β anomer to yield methyl β D fructofuranoside 1,6 P ₂. The occurrence of fructoside phosphorylation argues against the need for an intervening keto form to accomplish the transphosphorylation process. An absolute stereoselectivity of phosphofructokinase for the β anomer of fructose 6 P thus is indicated.