Studies on Limulus amoebocyte. Isolation and identification of a membrane-bound protein activator of cyclic nucleotide phosphodiesterase from Limulus amoebocyte.
A protein isolated from Limulus polyphemus amoebocyte activates the hydrolysis of cyclic AMP by phosphodiesterase. The protein activator, like calmodulin, requires Ca2+ for its activity and is antagonized by calmodulin-modulating protein from bovine brain. 2-Chloro-10-(3-aminopropyl)-phenothiazine, a compound known to bind calmodulin, also inhibits the effect of the protein activator. This Limulus protein activator is an acidic protein with high percentage of glutamate and aspartate; it contains trimethyllysine, a characteristic amino acid found in all calmodulin. It is different from calmodulin isolated from other species, however, in its molecular weight (4 to 5 times greater), amino acid composition, antigenicity, and binding ability on 2-chloro-10-(3-aminopropyl)-phenothiazine affinity column chromatography. The amino acid composition, gel electrophoresis pattern, and molecular weight of this protein activator are indistinguishable from endotoxin-binding protein which we isolated previously by other independent methods. Immunologic studies demonstrate that these two proteins are essentially identical. The endotoxin-binding protein thus has the dual functions of binding endotoxin, and showing calmodulin-like activity. It may play an important role in degranulation of Limulus amoebocytes which is induced by minute amounts of gram-negative bacterial endotoxin.
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism*; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001921:Brain; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000494:pharmacology; D002417:Cattle; D002462:Cell Membrane / Q000032:analysis; D004789:Enzyme Activation; D005455:Fluorescent Antibody Technique; D006737:Horseshoe Crabs / Q000201:enzymology*; D005779:Immunodiffusion; D008565:Membrane Proteins / Q000302:isolation & purification / Q000502:physiology*
D000596:Amino Acids; D002147:Calmodulin; D008565:Membrane Proteins; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D002118:Calcium