Cycloheximide

Cycloheximide is an inhibitor of protein biosynthesis in eukaryotic organisms, produced by the bacterium Streptomyces griseus. Cycloheximide exerts its effect by interfering with the translocation step in protein synthesis (movement of two tRNA molecules and mRNA in relation to the ribosome) thus blocking translational elongation. Cycloheximide is widely used in biomedical research to inhibit protein synthesis in eukaryotic cells studied in vitro (i.e. outside of organisms). It is inexpensive and works rapidly. Its effects are rapidly reversed by simply removing it from the culture medium.

Due to significant toxic side effects, including DNA damage, teratogenesis, and other reproductive effects (including birth defects and toxicity to sperm ), cycloheximide is generally used only in in vitro research applications, and is not suitable for human use as a therapeutic antibiotic compound. Although it has been used as a fungicide in agricultural applications, this application is now decreasing as the health risks have become better understood.

Cycloheximide is degraded by alkali (pH > 7), decontamination of work surfaces and containers can be achieved by washing with a non-harmful alkali solution such as soap.

Since cycloheximide is an effective inhibitor of protein biosynthesis in Eukaryotes only, it may be used to distinguish between genes expressed in organelles and genes expressed in the nucleus. Genes expressed in the eukaryotic nucleus will not be expressed in the presence of cycloheximide. Conversely, organelle transcription is unaffected by cycloheximide, and organelle genes will continue to be expressed.

In vitro applications
Cycloheximide can be used as an experimental tool in molecular biology to determine the half-life of a protein. Treating cells with cycloheximide in a time-course experiment followed by Western blotting of the cell lysates for the protein of interest can show differences in protein half-life. Cycloheximide treatment provides the ability to observe the half-life of a protein without confounding contributions from transcription or translation.