Ca2+-activated protease activity in frog sciatic nerve: characterization and effect on rapidly transported axonal proteins.
Protease activity was studied in the frog sciatic nerve. The activity was measured as the release of TCA-soluble radioactivity from either 3H-labelled proteins transported by rapid axonal transport (AXT) or 3H-labelled ganglionic proteins. In nerve homogenates containing transported substrates, protease activity exhibited two peaks, one around pH 5 and one around pH 8. Ca2+ at 100 microM or higher concentrations only stimulated the latter, which was inhibited by 1 mM parachloromercuric benzoate, a sulphydryl reagent, but unaffected by ATP (1 mM). The proteolytic activity was recovered in the 10(5) g supernatant of the homogenate. In desheathed nerves containing 3H-labelled transported proteins, the protease activity could be activated by exposing the nerve to a Ca2+-ionophore, X-537 A, or to an elevated Ca2+-concentration (50 mM). These conditions were also shown to increase the influx and efflux of 45Ca2+ in the nerves. The results indicate the presence within axons of a Ca2+-activated soluble protease, which degrades rapidly transported proteins. The finding that the protease degraded ganglionic soluble proteins to about the same extent suggests a broad substrate specificity. The present system should be useful for further characterization of protease activity during various physiological conditions.
Kanje
M
M
Lazarewicz
J
J
Ekström
P
P
Edström
A
A
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000378:metabolism*; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism / Q000502:physiology; D002154:Calpain; D002729:Chloromercuribenzoates / Q000494:pharmacology; D010450:Endopeptidases / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D011893:Rana esculenta; D011896:Rana temporaria; D012584:Sciatic Nerve / Q000201:enzymology*; D013997:Time Factors; D014018:Tissue Distribution; D020245:p-Chloromercuribenzoic Acid
D002729:Chloromercuribenzoates; D009419:Nerve Tissue Proteins; D020245:p-Chloromercuribenzoic Acid; D000255:Adenosine Triphosphate; D010450:Endopeptidases; D002154:Calpain; D002118:Calcium