Cell-free protein synthesizing systems from Vicia faba (L)

Abstract

Vicia faba (L) seeds form protein as their major food reserve. The two major storage proteins, vicilin and legumin, which account for up to 20% dry weight of the mature seed are formed within a comparatively short period during seed development, and during this period, a significant part of the total metabolism of the cell is directed towards their synthesis. An active cell-free amino acid incorporating system has been isolated from developing seeds, and its conditions of activity determined in in vitro incubations using polyuridylic acid as a messenger. Bacterial contamination of the incubations was low. The activity of this system in amino acid incorporation is compared with other in vitro systems from plants. Microsomes, enzyme fractions and tRNA were prepared from developing seeds of different ages, and the above system-was used to assay changes in the amino acid incorporating activity of components from different ages of seeds, to see if any correlation could be found between the changes in the in vivo protein synthetic activity during seed development with the changes in the in vitro efficiency of the components in incorporation. Rates of in vitro amino acid incorporation were compared with the estimated rate of in vivo synthesis of the storage proteins. The changes in the in vitro amino acid incorporating activity are discussed with reference to the anatomical changes occurring during seed development, as seen in electron micrographs of developing seeds, and in particular with reference to the changes in the free and membrane bound ribosome content. Further evidence for the role of the membrane bound ribosomes in storage protein synthesis is presented.