The Incorporation of14C into the Protein of Particles Isolated from Plant Cells

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Abstract
The incorporation of 14C from labelled fructose, succinate, urea, and proline, by particulate preparations from dormant and tissue-cultured carrot cells, is examined. It is shown that 14C is incorporated readily from proline, and less readily from fructose. No significant incorporation occurs from succinate or urea. No differences are noted between the two kinds of preparation. It is concluded that the incorporation of 14C does not depend on prior transfer of the label to carbon dioxide followed by fixation of carbon dioxide, since the particles do not incorporate 14C from supplied carbon dioxide. Incorporation of 14C by various fractions of dormant carrot tissue is examined, and it is established that the greatest incorporation per mg. nitrogen occurs in particles isolated at 10,000 g. A total cell homogenate fails completely to incorporate 14C from proline into protein, and this may be due to suppression of the activity of the particles by a constituent of the supernatant liquid. The presence of coconut milk reduces the incorporation of 14C from proline by particles sedimented at 10,000 g, and addition of a protein hydrolysate reduces it further. Hydroxy-proline does not appear to compete with proline for incorporation, and in this respect the paniculate preparations contrast with whole cells. Particles from carrot tissue are shown to be more active in incorporating 14C from proline than are particles extracted by the same procedure from red beet roots, potato tubers, and skunk cabbage inflorescences. They are, however, considerably less active than a mitochondrial preparation from rat liver. It is demonstrated by paper chromatography that the bulk of the 14C incorporated in the particles from carrot cells remains in proline and there is little or no conversion of proline to hydroxyproline in the preparations. The nature of the particles employed in this investigation is discussed, and their metabolism considered, in relation to the structure and activity of whole cells.