The Use of C14-Proline by Growing Cell: Its Conversion to Protein and Hydroxyproline

Abstract

C¹⁴-proline is readily absorbed by growing tissue cultures of carrot root phloem and of potato tuber in experiments carried out under aseptic conditions. The C¹⁴-proline rapidly enters into the protein of the tissue, appearing there in as short a period as 15 minutes, and, thereafter, the amount incorporated into the protein bears a linear relation to time. Virtually all the C¹⁴ appears in the protein hydrolysate in the form of proline and hydroxyproline. It is shown that the conversion from proline to hydroxyproline occurs after the C¹⁴-proline is combined into the protein and that this conversion proceeds progressively with time. The ratio of C¹⁴ as proline to C¹⁴ as hydroxyproline declined progressively from a value of 4.0 after 30 minutes of contact and seemed to become stabilized eventually at 0.7. C¹⁴-hydroxyproline, which can be absorbed by the tissue, seems not to be incorporated into the protein as such. The protein moiety which contains the C¹⁴-hydroxyproline from C¹⁴-proline represents a stable protein which is not metabolized and whose carbon does not ‘turn over’. This inert protein seems to be characteristic of cells which are in rapid division under the influence of coconut milk or are synthesizing protein in response to other stimuli such as the events at a cut tissue surface. The protein in question seems to be present mainly in the cytoplasm rather than in its paniculate inclusions. These results are compatible with earlier views which require that part of the protein in the cell ‘turns over’ its carbon, whereas another part does not do so.