IPTG storage: Store in a dark place at -20 ℃ and have a shelf life of up to 2 years. However, the culture medium containing IPTG needs to be stored in a dark place at 4 ℃ and must be used within 1 week. This is because IPTG (isopropylthio)- β- D-galactoside is an inducer used to induce the expression of lactose operon (LAC). In the lac operon, when there is no exogenous inducer present, the expression of the lacZ, lacY, and lacA genes is inhibited by repressor proteins and cannot be expressed. When the inducer IPTG is added, it binds to the repressor protein, releasing its inhibitory effect on three genes and allowing them to be expressed.

The stability of IPTG varies at different temperatures. Under the condition of -20 ℃, IPTG can be stably stored for 2 years. This is because low temperature can slow down the rate of chemical reactions and reduce the possibility of IPTG degradation. In addition, avoiding light is also necessary as it may cause the decomposition of IPTG.

However, for culture media containing IPTG, it needs to be stored at 4 ℃ and must be used within 1 week. This is because the culture medium contains other components such as proteins and enzymes, which may affect the stability of IPTG. At higher temperatures, these components may react with IPTG, causing it to lose its inducing effect. Therefore, in order to maintain the effectiveness of IPTG, it is necessary to store it separately from the culture medium and mix it when needed.

In summary, the correct storage conditions are crucial for maintaining the effectiveness of IPTG. Understanding these conditions can help researchers better design experiments, ensuring the accuracy and reliability of experimental results. Meanwhile, for laboratory staff, it is also very important to understand these storage conditions, as they need to ensure that the reagents and culture media in the laboratory are properly processed and stored.