Which of the following is the measure of catalytic efficiency of an enzyme?

The kinetic parameters kcat and Km are useful for the study and comparison of different enzymes, with simple or complex reaction mechanisms. kcat and Km are used as an estimate for the kinetic efficiency of enzymes, but either parameter alone is insufficient for this purpose. For instance, two enzymes catalyzing different reactions may have the same kcat (turnover number), yet the rates of the uncatalyzed reactions may be different and thus the rate enhancements brought about by the enzymes may differ greatly. Hence, the best way to measure the catalytic efficiencies of different enzymes is to compare the ratio Kcat/Km for the two reactions. This parameter, is called the specificity constant, is the rate constant for the conversion of E + S to E + P when << Km.