Solubility and stability properties of the melanin-dispersing substances from the eyestalks of the fiddler crab,Uca pugilator

Abstract

1. Extracts of fresh, freeze-dried, and heat-dried eyestalks prepared directly in physiological saline evoked nearly identical melanin-dispersing responses. The highly active ethanol-soluble fraction extractable from fresh eyestalks ofUca was to a great extent unextractable after the eyestalks were freeze-dried, heat-dried, or pretreated with a variety of organic solvents, whereas the melanin-dispersing substance in the ethanol-insoluble fraction of the eyestalk was resistant to these treatments. The melanin-dispersing substance obtained by direct extraction of the eyestalk in water is more resistant to treatment with organic solvents than the substance present in the ethanol-soluble fraction. 2. The melanin-dispersing activities of the eyestalk material soluble in various solvents showed no overall relationship with the dielectric constants of the solvents used. However, the melanin-dispersing activity was related to the dielectric constants of the normal alcohols used in the following decreasing order: methanol>ethanol>propanol>butanol>amyl alcohol. 3. Ether and isopropyl ether destroyed most of the melanin-dispersing material present in the ethanol-soluble and water-soluble fractions of the eyestalk, possibly due to excessive oxidation. 4. The melanin-dispersing material in the ethanol-soluble fraction of the eyestalk is greatly destroyed by heat. In contrast, the melanin-dispersing material in the water-soluble fraction of the eyestalk is resistant to heat. 5. The possibility that two melanin-dispersing substances are present in the eyestalks ofUca is considered and discussed.