[Choice of the association model of rabbit muscle phosphofructokinase using mathematical modeling]

The sedimentation behaviour of the subform of rabbit muscle phosphofructokinase specifically eluted from DEAE cellulose by citrate was studied in different media by velocity experiments. The measured sedimentation coefficients of different components in the system can be classified into 12 groups, which is indicative of a complex multistep association process of the enzyme (with more than 3 oligomers). The concentration dependence of weight average sedimentation coefficient of phosphofructokinase was a studied. The choice of the probable association model of phosphofructokinase oligomers at low protein concentration was accomplished by means of computer simulation of the association process. Of 26 closed association models tested 14 models with 2 or 3 association constants are indistinguishable in view of Student's t-criterion of significance. All uniparametric association models studied significantly inferior approximate the experimental data. It is supposed that the dimer is not the structural unit of polymerization. Having this in mind and taking into account the demand for the multistep process, one may consider as most probable only 8 models of phosphofructokinase association, namely monomer-dimer-trimer-tetramer-monomer-dimer-tetramer-octamer (with 3 association constants) and linear polymerization up to the octamer with 2 association constants, where the "monomer" of association may be defined as trimer, tetramer or hexamer of subunits.