Postnatal Changes in Enzyme Activities in Synaptosomes Isolated from Hamster Optic Nerve Endings

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Abstract
Subsynaptosomal fractions isolated from optic terminal nuclei of adult and neonatal hamsters exhibited developmental changes in specific density, mitochondrial activity and K+-stimulated, ouabain-inhibited p-nitrophenylphosphatase (K-pNPPase) activity around the time of eye opening. The specific activity of K-pNPPase was 6- to 7-fold higher after eye opening (14-16 days postnatal). A significant proportion of high-specific-activity K-pNPPase was recovered from the lightest subsynaptosomal fraction at all ages. This fraction contained very little external membrane by galactose oxidase-NaB3H4 labeling, suggesting that it may represent an internal pool, possibly the axonally transported form of the enzyme. Synaptic mitochondrial cytochrome c oxidase activity also approximately doubled in 12-16 days. The specific density of the external membrane increased more slowly, banding at 1.0 M sucrose at 12 and 16 days and 1.2 M in adults. These maturational events may reflect increased energetic needs of optic nerve endings following eye opening.