E1 Enzymes (Ubiquitin-activating enzymes)

E1 enzymes, or ubiquitin-activating enzymes, are the first step in a process that tags proteins for various fates, such as degradation. They activate ubiquitin, a small protein, by attaching it in an energy-dependent manner. This activation involves forming a high-energy bond between ubiquitin and E1. Once activated, the ubiquitin is transferred to other enzymes (E2 and E3), which help attach it to specific target proteins. This tagging process plays a critical role in regulating protein levels and maintaining cellular health by marking damaged or unneeded proteins for destruction or other cellular responses.