title: Chromomycin A3
text: # Chromomycin A3
  
  Chromomycin A3 $(CMA_3)$ or Toyomycin is an anthraquinone antibiotic glycoside produced by the fermentation of a certain strain of Streptomyces griseus (No. 7).
  
  ## Fluorescence properties
  
  In the presence of $Mg^{2+}$ ions, Chromomycin $A_3$ binds reversibly to DNA, preferentially to contiguous G/C base pairs.
  
  When bound to DNA, Chromomycin $A_3$ has a maximum excitation wavelength of 445 nm (blue), and a maximum emission wavelength of 575 nm (yellow).
  
  ## Uses
  
  * in-vitro membrane-impermeant G/C-specific fluorescent DNA-binding dye.
  * in-vitro antibiotic of gram-positive bacteria, through inhibition of the incorporation of $P_i$ in the RNA.
  * in-vitro anticancer drug that inhibits RNA synthesis.
  * Evaluation of male fertility: Chromomycin $A_3$ and protamines compete for the same binding sites in the DNA, so $CMA_3$ positivity in spermatozoa reflects protamine deficiency (affecting sperm morphology and decreasing fertility).
  