Isolation strategies for finding bioactive compounds: Specific activity vs. total activity

There are two major strategies for isolation of bioactive natural products. One is to find compounds with high specific activity (biological activity per unit weight of the compound). This leads to the discovery of the most active compounds present in an organism with low EC₅₀ (effective concentration of the compound to induce half-maximum action). In the other strategy, compounds with high total activity (biological activity per unit weight of the organism containing the bioactive compound), causing a particular phenomenon, are isolated. In this strategy, EC₅₀ of the compound is not necessarily low. The total activity is determined by the specific activity and concentration (or content) of the compound in the organism, and this could explain the role and influence of the compound in the phenomenon. Differences between the two strategies and the importance of the choice for the right one to apply are emphasized, and applicatory examples complementary to each strategy are presented. The author proposes to use the terminology and concept of "total activity" and "specific activity" to avoid confusion in scientific discussions.