The limitations of chlorotetracycline as a fluorescent probe of divalent cations associated with membranes.

The interaction of chlorotetracycline with magnesium chloride, detergents and ATP and ADP has been investigated. At various pH the fluorescence of chlorotetracycline, or the chlorotetracycline complex, is enhanced in the presence of the negatively charged detergent sodium dodecyl sulphate, the uncharged detergent Triton X-100, or the positively charged detergent cetyltrimethylammonium bromide. Also ternary fluorescent complex is formed between chlorotetracycline, magnesium and ATP or ADP. In a biological membrane, it would not seem possible to distinguish between the fluorescence signal arising from chlorotetracycline acting as a probe of divalent cations bound to specific sites on the membrane and that arising from the complex of chlorotetracycline with divalent cations acting as a probe of neutral or negative regions of the membrane.