The Incorporation of14C-Proline into the Proteins of Growing Cells: I. EVIDENCE OF SYNTHESIS IN DIFFERENT PROTEINS AND CELLULAR COMPONENTS

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Abstract
14C-proline was supplied to aerated potato disks, in which cell division was occurring, and also to rapidly growing potato carrot explants. It was absorbed and incorporated into all the subcellular protein fractions examined, including the electrophoretically distinguishable fractions of the soluble protein of the potato disks and explants. The 14C-proline was partially converted to 14C- hydroxyproline in all the protein fractions, except for one of the soluble protein fractions of potato explants and the soluble proteins of one set of potato disks. Most of the 14C-proline and 14C-hydroxyproline contained in the tissue was found in the soluble protein and also in the cellular fragments obtained by centrifugation at 500 g. The relative importance of the soluble protein in the incorporation of 14C-proline and its conversion to 14C-hydroxyproline was greatest over a short period of a few hours of contact with the 14C-proline supplied. Over a longer period (70 hours) the cellular fragments (500 g) had become the most important and contained over 40 per cent. of the total 14C, and more than 60 per cent. of the 14C-hydroxyproline, in the protein of the tissues. In the soluble fraction of potato explants, seven protein bands were distinguishable on electrophoresis. A different but characteristic value of the ratio 14C-hydroxyproline to 14C-proline was associated with each protein band, except for the one region where 14C-hydroxyproline did not occur. The basic proteins (i.e. those moving towards the cathode) were the most active in the incorporation of 14C-proline and its conversion to 14C-hydroxyproline. The rather general distribution of the 14C-hydroxyproline is noted and the possible siginificance of the basic proteins and the proteins associated with the cellular fragments (500 g) is considered in relation to the growth, cell division, and cell wall formations which occurs in the rapidly growing tissue cultures.