Antimicrobial activity in the skin of the channel catfish Ictalurus punctatus: characterization of broad-spectrum histone-like antimicrobial proteins

Three antibacterial proteins were isolated from acid extracts of channel catfish (Ictalurus punctatus) skin by cation exchange chromatography and reverse-phase high-pressure liquid chromatography. The molecular masses of the proteins were 15.5, 15.5 and 30 kD as determined by SDS-polyacrylamide gel electrophoresis. Mass spectrometry, amino acid composition and amino acid sequence data suggest that the most abundant protein is closely related to histone H2B. The H2B-like protein was inhibitory to Aeromonas hydrophila and Saprolegnia spp., which are important bacterial and fungal pathogens of fish. These findings suggest that histones may be important defensive molecules in fish. Received 22 December 1997; received after revision 5 March 1998; accepted 5 March 1998     

Intracellular pH of Limulus ventral photoreceptor measured with a double-barrelled pH microelectrode

Summary The intracellular pH of the Limulus ventral photoreceptor was measured with a double-barrelled pH microelectrode and found to be 7.01±0.04 SE (n=9).This work was supported by the Swiss National Science Foundation, grants Nos. 3.634.075 and 3.128.73.Acknowledgments. We thank Drs L. R. Pucacco and N. W. Carter for technical advice and a gift of pH glass. We also thank Drs M. Tsacopoulos and F. Baumann for helpful discussion.