PubMed · 14803060
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K FELIX, H FISCHER, A KREKELS, H M RAUEN. 1950. [Clupeine].. https://pubmed.ncbi.nlm.nih.gov/14803060/
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The antimicrobial effect of protamine (clupeine) on a range of gram-positive and gram-negative foodborne pathogens and spoilage bacteria, was evaluated using an agar dilution assay and a broth dilution assay with Alamar Blue as growth indicator. Protamine was tested alone at concentrations from 0 to 10,000 microg/ml, and in combination with EDTA (0.9 mM). Assays were performed at 5 degrees C, 10 degrees C, 18 degrees C and 30 degrees C to test the effect of temperature. Minimum inhibitory concentration (MIC) values ranged from 10 microg/ml for Brochothrix thermosphacta to no inhibition at 10,000 microg/ml for bacteria such as Aeromonas hydrophila, proteolytic strains of Clostridium botulinum, Hafnia alvei and Morganella morganii. The minimum bactericidal concentrations (MBCs) were generally higher than MICs. In combination with EDTA, MICs of protamine decreased for gram-negative test strains, whereas EDTA alone inhibited gram-positive strains. The effect of assay incubation temperature was variable and not clear for most strains. Concentrations of 100-750 microg/ml protamine inhibited the five non-proteolytic C. botulinum strains, while none of the eight proteolytic strains was inhibited, indicating the possible role of proteolytic enzymes in protecting cells from protamine. Clearing zones, indicative of proteolytic activity, were observed in the opaque TSB-agarose around colonies of some but not all protamine-resistant bacteria, suggesting that this is not the only resistance mechanism. Addition of 5% (w/v) gelatin to study the effect of an increased protein concentration in the agar dilution assay showed that electrostatic interactions between protamine and the protein decreased the antimicrobial efficacy of the peptide.
Conjugates of fluorescein isothiocyanate with clupein YI, YII and Z, the protamines from Clupea palasii, were prepared and their fluorescence utilized to determine the rotational relaxation times of the proteins. All conjugates exhibited single component lifetimes near 4.05 ns. Linear isothermal Perrin plots were obtained for all conjugates; these data indicated rotational relaxation times of 3.33 ns for clupein YI and YII and 3.19 ns for clupein Z. These results and the results from our previous studies lead us to postulate globular conformations for the three proteins with hydrated molecular diameters of 22 A. Based on these findings a three dimensional model for Clupein YII is proposed.
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