Bacteriochlorophyll, Fatty-Acid, and Protein Synthesis in Relation to Thylakoid Formation in Mutant Strains of Rhodospirillum rubrum

Mutant strains of Rhodospirillum rubrum are isolated which are blocked in different stages of pigment synthesis. In these strains the morphogenesis of thylakoids and the pigment production are investigated. Concerning bacteriochlorophyll synthesis two groups of mutants are separable. The members of the first group synthesize bacteriochlorophyll. Some of these mutants excrete bacteriopheophytin. The strains of the second group are not able to synthesize bacteriochlorophyll. Members of both groups excrete bacteriochlorophyll precursors into the cultural medium. These pigments were identified by their spectral properties as Mg-2,4-divinyl-pheoporphyrin a(5)-monomethylester, pheophorbide a, and 2-devinyl-2-hydroxyethyl-pheophorbide a. Thylakoids are only formed by those strains which are able to synthesize bacteriochlorophyll. However, small amounts of bacteriochlorophyll can be produced without a concomitant thylakoid synthesis. The fatty-acid pattern in some mutants is modified quantitatively. However, the results do not indicate any correlation between disturbance of thylakoid morphogenesis and a deviation of fatty-acid composition. Fatty acids seem to have no special functions in thylakoid morphogenesis. The membranes of the mutants were isolated, split into protein subunits, and these were separated by disc electrophoresis. A characteristic protein pattern, first of all a high content of fraction E, is correlated with the ability to form thylakoids. In addition, all mutants which synthesize bacteriochlorophyll contain a fast-migrating membrane protein (zone G). The results suggest that the whole bacteriochlorophyll-protein complex is necessary for thylakoid formation.     

Galactose Transport in Saccharomyces cerevisiae III. Characteristics of Galactose Uptake in Transferaseless Cells: Evidence Against Transport-Associated Phosphorylation

The characteristics of the inducible galactose transport system in bakers' yeast were studied in uridine diphosphate, galactose-1-phosphate uridylyl-transferaseless cells. Transferaseless cells transport galactose at the same initial rate as wild-type cells and accumulate a mixture of free galactose and galactose-1-phosphate. The addition of ¹⁴C-labeled galactose to cells preloaded with unlabeled galactose and galactose-1-phosphate results in a higher rate of labeling of the free-sugar pool than of the galactose-1-phosphate pool. These results support other evidence that galactose uptake in bakers' yeast is a carrier-mediated, facilitated diffusion and that phosphorylation is an intracellular event after uptake of the free sugar.