Protein Turnover in the Primary Leaves ofPhaseolus vulgaris

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Abstract
A technique which measures the change in 2-3H content of protein with time by racemization of the protein hydrolysate with acetic anhydride was employed to measure protein turnover in the primary leaves of Phaseolus vulgaris var. The Prince. Plants were grown in liquid culture and the radioactivity was introduced through the roots in the form of tritiated water. Substantial quantities of 1H2O (1 mCi ml−1), a 48 h exposure to 3H2O, together with detopping of the plant (which stimulates resumption of protein synthesis as shown by a 3-fold increase, over normal plants, in 3H incorporated into different protein fractions in the 24 h immediately following detopping) were required to obtain manageable amounts of label incorporated into mature leaves. Under these particular conditions the half-life, the time required for half the protein molecules initially present to be degraded, of chloroplast coupling factor (CF1) was estimated as 1.53 d, of a total soluble protein fraction (TSP) as 1.9 d, and of a chloroplast lamellae fraction as 7.65 d.

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