The Cytoplasmic Protein Component of Green Leaves

Citation

Eggman, William Luther (1953) The Cytoplasmic Protein Component of Green Leaves. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/MQ5F-JT09. https://resolver.caltech.edu/CaltechETD:etd-05082003-154241

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The soluble cytoplasmic proteins of the leaves of dicotyledonous plant species have been characterized as to their chemical and physical chemical properties. Elephoretically, the proteins migrate as a single major component and from one to six minor components, the number depending upon the species. The principal component has a mobility of ca. ?5.0 to ?5.5 x 10[superscript ?5] [. . .] K-maleate buffer at pH 7.0, and constitutes ca. 50 to 80 per cent of the total protein. In the analytical ultracentrifuge, the proteins are resolved into two components; a high-molecular weight, apparently homogeneous component with a corrected sedimentation, constant of 19S which constitutes ca. 30 to 50 per cent of the total protein, and a low-molecular weight heterogeneous, fraction which contains the enzymatic activity. Chemically, the cytoplasmic proteins contain 13 to 15 per cent nitrogen and from 0.1 to 0.8 per cent phosphorus. This protein-bound [phosphorus] was found to be associated with the 19S component of cytoplasm in the form of ribonucleic acid. The principal component of cytoplasm is, therefore, a nucleoprotein. The nucleotide composition of the ribonucleic acid in the cytoplasms of leaves of different plant species and in leaves of different physiological ages but from the same plant species were studied. The composition varies with the plant species but not with physiological age. The effects of pH, of temperatures from 0[degrees] C. to 37[degrees] C., of dialysis and of storage at ?20[degrees] C. upon the stability of whole cytoplasm preparations was studied by chemical and ultracentrifugal analysis. Acidity greater than pH 6.5 and storage at ?20[degrees] C. for extended periods preferentially denatures the protein moiety of the nucleoprotein component, while dialysis or incubation at room temperatures for short periods of time causes the loss, apparently by enzymatic degradation, of the ribonucleic acid moiety. No method of entirely preventing the loss of nucleic acid was found, although maintenance of a low temperature partially suppresses it. A differential sedimentation procedure capable of preparing high-molecular weight fractions of cytoplasm (Fraction I protein preparations) containing only 5 to 10 per cent of low-molecular weight contaminants was developed when classical methods of chemical fractionation proved unsuitable. Such preparations were used to determine the physical properties of the nucleoprotein component. The nucleoprotein components of spinach and tobacco have been shown to be closely similar, although certain physical properties of the nucleoprotein, such as partial specific volume, sedimentation constant and molecular weight, are dependent on the ribonucleic acid content. The molecular weight of the nucleoprotein component in a particular preparation containing 11 per cent nucleic acid is estimated to be 360,000, based on determination of the partial specific volume and the sedimentation constant of this preparation together with an estimation of the frictional coefficient from a deduced shape factor and an assumed hydration value. Fraction I protein preparations always contain high-molecular weight components that are not initially present in whole cytoplasm. It is shown that these components probably have their origin in aggregation of the nucleoprotein component.

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