PMID: 33988Mar 25, 1979

Binding of regulatory ligands to rabbit muscle phosphofructokinase. A model for nucleotide binding as a function of temperature and pH

The Journal of Biological Chemistry
D W Pettigrew, C Frieden

Abstract

The binding of nucleoside triphosphates to rabbit muscle phosphofructokinase has been determined in 0.05 M phosphate buffers by changes in intrinsic protein fluorescence and by direct binding measurements. These experiments have been performed over a wide range of pH, temperature, and effector concentration. Quenching of protein fluorescence is shown to measure binding of nucleotides to a site which is not the active site but rather a site responsible for inhibition of the kinetic activity. This site is relatively specific for either ATP or MgATP with free ATP binding about 10-fold more tightly than MgATP. A model to describe binding to this site as a function of pH and temperature is proposed. This model assumes that the apparent affinity for ATP is determined by protonation of two ionizable groups (per subunit) and that ATP binds exclusively to protonated enzyme forms. Several ligands which affect the apparent affinity for nucleotide binding at the inhibitory site act by shifting the apparent pK of the ionizable groups. NH4+ and citrate do not influence nucleotide binding to the inhibitory site. At pH 6.9 in 0.05 M phosphate, low concentrations of MgATP or MgGTP enhance the protein fluorescence due to binding at the active si...Continue Reading

Related Concepts

ATP Binding
Magnesium GTP
Phosphate buffers
Allosteric Site
Nucleotide Binding
Adenosine Triphosphate, Magnesium Salt
Citrate Measurement
Phosphate Measurement
Fluorescence Spectroscopy
Phosphofructokinase

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