ACRIDINE ORANGE BINDING BY MICROCOCCUS LYSODEIKTICUS

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Abstract
Micrococcus lysodeikticus cells bind acridine-orange (AO) reversibly. The adsorption isotherm is consistent with a highly cooperative-type binding similar to that observed with polyadenylic-acid. The cells exhibit a strong buffering action on the concentration of free AO which remains constant (1 [mu]g /ml) over a range from 5 to 95% saturation of the cells by AO. The cells stain either fluorescent orange or green. The fraction stained orange is directly proportional to the quantity of dye adsorbed, indicating that these cells bind a fixed amount of AO (10% of dry weight). The green-stained cells contain less than 1% of the AO bound to orange-stained cells. The results suggest that the abrupt increase in amount of AO bound by the orange-stained cells occurs when the concentration of free AO reaches a threshold concentration. Similar results were obtained with Bacillus cereus. Mg increases the free AO concentration and the extent of binding capacity of the cells.