George Brawerman

Induced formation of ribonucleic acids and plastid protein in Euglena gracilis under the influence of light

Abstract 1. 1. Euglena cells grown in the light, which possess the photosynthetic apparatus, contain considerably more protein and RNA than the cells grown in the dark. 2. 2. The additional protein of the green cells is localized in the plastid fraction and appears to be part of the chloroplast structure. The additional RNA is distributed among the plastid, microsome and soluble fractions. 3. 3. During chloroplast formation in resting colorless cells exposed to light, the protein of the plastid fraction increases rapidly after a considerable lag period. The RNA of both the plastid and microsome fractions increases without apparent lag; its synthesis ceases before that of the plastid protein. 4. 4. The RNA produced during chloroplast formation may represent specific ribosomal material necessary for the synthesis of the plastid proteins.

On the formation of the TPN requiring glyceraldehyde-3-phosphate dehydrogenase during the production of chloroplasts in Euglena gracilis

Abstract Green Euglena cells possess a TPN-requiring glyceraldehyde phosphate dehydrogenase in addition to the DPN-requiring enzyme. The dark-grown, colorless cells contain only the DPN enzyme. In resting colorless cells exposed to light, the course of formation of the TPN enzyme follows closely that of chlorophyll. Removal of light during this process results a cessation of both enzyme production and chlorophyll synthesis. Cultivation of the green cells at 34° in the light produces an inhibition of chloroplast synthesis, and return of the cells to a lower temperature brings about a rapid resumption of chloroplast synthesis after a lag period of one to two days. The production of the TPN enzyme follows very closely that of the chloroplasts, both during the inhibition and the recovery. The synthesis of the DPN enzyme, on the other hand, is linked to the multiplication of the cells during this process.

Changse in protein and ribonucleic acid during the formation of chloroplasts in Euglena gracilis

Abstract Etiolated Euglena gracilis cells can form chloroplasts in the absence of growth and without the net synthesis of protein and ribonucleic acid. During this process, approximately 17% of the cellular proteins appear in the chlorplasts fraction. Only the supernatant fraction shows a significant decrease, and it is tentatively concluded that the chloroplastic proteins originate in the latter fraction. The ribonucleic acid distribution in the cell is little changed. The development of chloroplasts appears to be linked with a stimulation of the uptake of adenine by the ribonucleic acid and of leucine by the protein. These stimulations are apparent in all fractions of the cells. It is concluded that no preferential synthesis of protein and RNA occurs in the chloroplasts during their final development. The formation of specific ribonucleic acid molecules during the process is indicated.

On the distribution and biological significance of the nucleoside phosphotransferases

Abstract Nucleoside phosphotransferases were found in a large variety of plant and animal tissues. In plants and bacteria, only 5′-nucleotides are formed, while in animals small amounts of the 3′-isomers are also produced. The rates of phosphate transfer from phenylphosphate and 5′-inosinic acid are of the same order of magnitude in plants, bacteria and protozoa, but in the mammals transfer from the nucllotide is much slower. The enzyme is unevenly distributed in the organs of the rat, with the highest activities in liver, spleen and kidney, and the lowest in muscle. The bulk of the enzymic activity is localized in the cytoplasmic particles. Considerable increases in the activity of the enzyme occur during germination of wheat, regeneration of rabbit muscle, and bacterial growth. The results point to an active role of the nucleoside phosphotransferases in nucleotide biosynthesis.

Relation of ribonucleic acid to the photosynthetic apparatus in Euglena gracilis

Abstract The ribonucleic acids of green and etiolated Euglena gracilis cells show small but definite differences in their nucleotide distribution. The green organisms have a higher proportion of adenylic and uridylic acids and a lower content of cytidylic and guanylic acids. Permanently bleached cells resemble the etiolated organisms in their ribonucleic acid composition. The differences in the ribonucleic acids of the green and etiolated oragnisms are probably related to the differenced in structure and metabolism of the two types of cells. Two additional nucleotides are present in small amounts in the ribonucleic acid of Euglena gracilis. One of them is probably identical with a nucleotide recently found in the ribonucleic acids from other organisms and the second one is unknown.

On the desoxypentose nucleic acids from several microorganisms

The isolation of the desoxypentose nucleic acids of three microorganisms, viz. Serratia marcescens, a facultatively autotrophic hydrogen organism Bacillus Schatz, and Hemophilus influenzae, type c, is described. The composition of these substances with respect to the contents of adenine, guanine, cytosine, and thymine was determined; this led to their classification in regard to the DNA types to which they belong. A procedure for the separation of the purines adenine and guanine from the pyrimidines cytosine and thymine by adsorption chromatography on filter paper with water as the solvent has been developed.

On the synthesis of nucleotides by nucleoside phosphotransferases

Abstract Various tissues contain enzymes catalyzing the transfer of phosphoric acid from low-energy organic phosphates to nucleosides, thereby effecting the synthesis of nucleotides. The behavior of the enzyme present in malt is studied with respect to pH, acceptor and donor concentrations, and inorganic phosphate effects. The enzymes, for which the designation nucleoside phosphotransferases is proposed, appear to be specific for nucleosides. Three types of enzymes are described that differ in their specificities with respect to donors, acceptors and nucleotide isomers formed. The possible role of the nucleoside phosphotransferases in the biosynthesis of nucleic acids is discussed.

On the nucleic acids of green and colorless Euglena gracilis: isolation and composition of deoxyribonucleic acid and of transfer ribonucleic acid.

Abstract The isolation and composition of two species of nucleic acid, DNA and transfer RNA, from Euglena gracilis are described. Preparations from green and colorless cells of this organism did not differ in nucleotide composition. Several minor componentswere identified in hydrolysates of the transfer RNA. The DNA was found to contain more than 2 mole per cent of 5-methylcytosine and nearly equimolar amounts of the 4 major nitrogenous constituents. The sugar component of the DNA appears to be 2-deoxyribose.

Factors involved in the development of chloroplasts in Euglena gracilis.

The formation of chlorophyll in etiolated Euglena gracilis cells in the presence of light ceases abruptly when the light source is removed. It resumes only gradually when the culture is returned to light. The formation of chlorophyll is resting etiolated cells is unaffected by the “bleaching” temperature (34–35°). n nWhen growing green cells are subjected to the bleaching temperature, the formation of chloroplasts becomes linear with respect to time. Cell multiplication is still exponential, but smaller cell populations are obtained. n nCells undergoing the bleaching treatment are capable of resuming rapid chlorophyll formation when returned to normal temperature, but this capacity is lost after a prolonged treatment. The cells lose their ability to produce green colonies while still capable of returning their chlorophyll content to near-normal levels. n nThe bleaching treatment is interpreted as blocking the production of a catalyst required for the development of chloroplasts. The permanent loss of the chloroplast-forming ability is explained by ascribing a self-reproducing character to the cellular system that produces the catalyst. The bleaching treatment would affect both the activity and the self-reproducing capacity of this system.

A self-reproducing system concerned with the formation of chloroplasts in Euglema gracilis

Abstract Some strains of Euglena gracilis can permanently lose their ability to form chloroplasts when exposed to temperatures of 34–35° under growing conditions. If cells not yet irreversibly bleached are returned to lower temperatures, their rate of multiplication will determine whether the hereditary character will be lost or maintained. Rapidly growing cells become permanently bleached; cells dividing slowly or not at all rapidly regain their full ability to form chloroplasts. The results indicate the existence in Euglena of a self-duplicating system involved in the formation of chloroplasts. This system is characterized by a replication mechanism autonomous with respect to that of the cell as a whole and by a high susceptibility to environmental factors.