With the four mRMR lists, IFS was processed for each of the four sample groups, generating four IFS curves. Based on these results, we set k in FFS to be 16, 15, 14 and 19 for the data of enzymes, ion channels, GPCRs and nuclear receptors, respectively. Each of these figures is the index of the point of the first maximum value in the corresponding IFS curve. Shown in Fig. 1 are the four IFS curves with their corresponding FFS curves. The peaks of the four FFS curves finally reach the overall success rates of 85.48% with 32 features, 80.78% with 37 features, 78.49% with 30 features, and 85.66% with 32 features for enzyme group, ion channel group, GPCR group and nuclear receptor groups, respectively.