is a crystalline solid. Its solubility in water is minimal, 6 mg/L, and it may form colloidal suspensions. It is soluble in small alcohols, acetic acid, pyridine, poorly soluble in acetone and dioxane, and practically insoluble in diethylether and hydrocarbons. Pharmacological effect Gramicidins are ionophores. Their dimers form ion channel-like pores in cell membranes and cellular organelles of bacteria and animal cells. Inorganic monovalent ions, such as potassium (K+) and sodium (Na+), can travel through these pores freely via diffusion. This destroys vital ion concentration differences, i.e. ion gradients, between membranes thereby killing the cell via various effects. For example, ion leak in mitochondria halts mitochondrial ATP production in cells with mitochondria. Gramicidins can be used as topical antibiotic medications in low doses, even though they are potentially lethal for human cells. Bacteria die at lower gramicidin concentrations than human cells. Gramicidins are not used internally, as their significant intake may cause hemolysis and be toxic to the liver, kidney, meninges and olfactory system among other effects. References Polypeptide antibiotics Integral membrane proteins Antimicrobial peptides Formamides