Which of the following is NOT a feature of enzymes?

Enzymes are biological catalysts that speed up chemical reactions in living organisms. They have several notable features that facilitate their role in metabolic processes. One of the key characteristics of enzymes is that they are reusable; once a reaction occurs, they can be released unchanged and used again in subsequent reactions. Additionally, enzymes are highly specific, meaning that each enzyme typically catalyzes a particular reaction with a specific substrate due to the unique active site that fits only that substrate.

Another important aspect is that many enzyme-catalyzed reactions are reversible; this means that they can proceed in both the forward and reverse directions, depending on the concentration of substrates and products. This reversibility is vital for maintaining metabolic homeostasis in biological systems.

In contrast, the idea that enzymes are irreversible does not accurately reflect their nature in most cases. While some reactions facilitated by enzymes can be essentially irreversible due to thermodynamic properties or the formation of stable products, this is not a general feature of all enzymes. Many enzymes can catalyze reactions that can be reversed, which is fundamental to their role in biological pathways. Hence, the statement that "irreversible" is a feature of enzymes is not correct.