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 μM 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 105 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.

Ämnesord

NATURVETENSKAP  -- Biologi -- Cellbiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Cell Biology (hsv//eng)

Nyckelord

axonal transport

Ca

protease activity

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