Extracellular glycerophospholipid:cholesterol acyltransferase from Aeromonas salmonicida: activation by serine protease |
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Authors: | G. EGGSET,R. BJØ RNSDOTTIR,R. MCQUEEN LEIFSON,J. A. ARNESEN,D. H. COUCHERON,T. Ø . JØ RGENSEN |
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Affiliation: | Norwegian Institute of Fisheries and Aquaculture, Tromø, Norway;Institute of Medical Biology, University of Tromsø, Tromsø, Norway;The Norwegian College of Fishery Science, University of Tromsø, Tromsø, Norway |
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Abstract: | Abstract. Extracellular hacmolytic activities of Aeromonas salmonicida ssp. salmonicida to salmon red blood cells were shown to be due to different forms of the membrane-active enzyme glyccrophospholipidrcholcstcrol acyltransferase (GCAT). About 10% of the total haemolytic activity was due to a high molecular mass complex of LPS and GCAT (mol. mass >1000kDa), containing 35–50% neutral sugars and 1.5–2.0% protein. Some haemolytic activity (30–40% of total), corresponding to 50–70kDa by gel filtration, also contained GCAT-activity and may represent aggregated forms of GCAT. However, about 50% or more of the haemolytie activity was due to a protein of 26kDa free GCAT. Rabbit antibodies to GCAT neutralized the hacmolytic activity of both GCAT and GCAT-LPS. A transposon-produccd serinc protease negative mutant of the same A. salmonicida strain showed reduced haemolytic activity. The mutant produced a 38-kDa GCAT proform of low hacmolytic activity. The proform was processed by autogenous scrinc protease to a highly hacmolytic 26-kDa molecule with pl 6.3, similar to GCAT of the parent strain. The weakly haemolytic GCAT-LPS analogue of the mutant strain did not contain detectable amounts of the 26-kDa molecule and was not activated by proteases. |
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