title: Fish skeletal muscle contains a novel serine proteinase with an unusual subunit composition.
abstract: Proteinase I, an enzyme previously shown to be able to degrade contractile and cytoskeletal elements of white-croaker (Micropogon opercularis) myofibrils, was purified to apparent homogeneity by chromatography on DEAE-Sephacel, octyl-Sepharose CL 4B and arginine-Sepharose 4B. Its Mr was determined to be 269,000 by Sephacryl S-300 gel filtration. Under denaturing conditions, the enzyme dissociated into two subunits with Mr 20,000 and 15,500, in a molar ratio of 1.8:1. Proteinase I showed a pH optimum of 8.5. The enzyme was strongly inhibited by several serine proteinase inhibitors, whereas inhibitors of the other types of proteinases did not affect, or only scarcely affected, its activity. Several N-terminal-blocked 4-methyl-7-coumarylamide substrates having either arginine or lysine residues adjacent to the fluorogenic group were efficiently hydrolysed by the enzyme. These results indicate that proteinase I is a trypsin-like serine proteinase. The enzyme appears to be distinct from other proteinases previously described in skeletal muscle, and might be involved in the catabolism of myofibrillar proteins.
authors.affiliation: Instituto Nacional de Tecnología Industrial, Centro de Investigaciones de Tecnología Pesquera, Mar del Plata, Argentina.
authors.forename: E J
authors.initials: EJ
authors.lastname: Folco
authors.forename: L
authors.initials: L
authors.lastname: Busconi
authors.forename: C B
authors.initials: CB
authors.lastname: Martone
authors.forename: J J
authors.initials: JJ
authors.lastname: Sánchez
mesh_terms: D000818:Animals; D002845:Chromatography; D005399:Fishes / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D046911:Macromolecular Substances; D008970:Molecular Weight; D009132:Muscles / Q000201:enzymology*; D011480:Protease Inhibitors / Q000494:pharmacology; D011489:Protein Denaturation; D012697:Serine Endopeptidases / Q000302:isolation & purification* / Q000378:metabolism; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D046911:Macromolecular Substances; D011480:Protease Inhibitors; D015842:Serine Proteinase Inhibitors; D012697:Serine Endopeptidases