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A Study of the Aminoacyl-sRNA Synthetases of Phaseolus vulgaris in Relation to Germination

^a Botany Department, University College London, Gower St., London WC1, England

Optimum conditions for the extraction and assay by ATP-pyrophosphate exchange of the aminoacyl-sRNA synthetases of the various tissues of french bean (Phaseolus vulgaris) seeds and seedlings are described. Extracts of plumules, after passage through Sephadex G-25, were assayed for synthetase activity using an amino acid mixture as substrate, when a 30 to 100-fold stimulation of exchange above the endogenous level was obtained. This marked enhancement of exchange by added amino acids is largely attributed to the use of dilute extracts.

The total synthetase activity of the cotyledons was studied in relation to germination. Synthetase activity was highest in the dry cotyledon; activity decreased in proportion to the loss of protein during germination, i.e. the specific activity of the synthetases remained constant for at least the first 6 days of germination. With a few minor exceptions, the specific activity of the individual synthetases remained constant during germination.

The absolute activity of the synthetases of the plumule and radicle increased exponentially during germination. The specific activity of the synthetases in both tissues increased approximately 2-fold during the first 2 to 3 days of germination, then gradually decreased. However the asparaginyl-, valyl-, and histidinyl-sRNA synthetases in the plumule did not conform with this general pattern.

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