As described in enzymology, "induced fit" and "lock and key" models are used to explain the enzymic specificity of substrate. Previously, authors have studied the substrate specificity of Eisenia fetida protease I (FfP-I), showing that the interaction between this protease and its substrates underwent an "induced fit" followed by "lock and key" model. It needs further investigating whether this model is suitable for other enzymes. Here, the reactions of substrate-induced Eisenia fetida protease II (EfP-II), subtilisin (Sub) and lactate dehydrogenase (LDH) with their substrates were shown. EfP-II and Sub could not recognize chromozym U (CU) (P < 0.05) after incubated with chromozym TH (CTH) although the two proteases are natively able to react with both CTH and CU. The reaction followed an "induced fit-lock and key" pattern. In contrast, the two proteases were still able to react with CTH even though they have been incubated with CU. But neither earthworm protease nor subtilisin could recognize CU after CU and CTH treatment in turn, still suggesting that the reactions followed an "induced fit and then lock and key" procedure. Furthermore, the activity of LDH with lactate significantly decreased (P<0.05) after the enzyme had been incubated with pyruvate. The activity on the conversion of pyruvate into lactate was not significantly affected by a prior incubation with lactate. This suggests that the pyruvate-induced complementary conformation of LDH is more stable than lactate-induced conformation.