Evolution of eutherian cytochrome c oxidase subunit II: heterogeneous rates of protein evolution and altered interaction with cytochrome c

Cytochrome c oxidase subunit II (COII), encoded by the mitochondrial genome, exhibits one of the most heterogeneous rates of amino acid replacement among placental mammals. Moreover, it has been demonstrated that cytochrome c oxidase has undergone a structural change in higher primates which has altered its physical interaction with cytochrome c. We collected a large data set of COII sequences from several orders of mammals with emphasis on primates, rodents, and artiodactyls. Using phylogenetic hypotheses based on data independent of the COII gene, we demonstrated that an increased number of amino acid replacements are concentrated among higher primates. Incorporating approximate divergence dates derived from the fossil record, we find that most of the change occurred independently along the New World monkey lineage and in a rapid burst before apes and Old World monkeys diverged. There is some evidence that Old World monkeys have undergone a faster rate of nonsynonymous substitution than have apes. Rates of substitution at four-fold degenerate sites in primates are relatively homogeneous, indicating that the rate heterogeneity is restricted to nondegenerate sites. Excluding the rate acceleration mentioned above, primates, rodents, and artiodactyls have remarkably similar nonsynonymous replacement rates. A different pattern is observed for transversions at four-fold degenerate sites, for which rodents exhibit a higher rate of replacement than do primates and artiodactyls. Finally, we hypothesize specific amino acid replacements which may account for much of the structural difference in cytochrome c oxidase between higher primates and other mammals.      

Relationships among msx gene structure and function in zebrafish and other vertebrates

The zebrafish genome contains at least five msx homeobox genes, msxA, msxB, msxC, msxD, and the newly isolated msxE. Although these genes share structural features common to all Msx genes, phylogenetic analyses of protein sequences indicate that the msx genes from zebrafish are not orthologous to the Msx1 and Msx2 genes of mammals, birds, and amphibians. The zebrafish msxB and msxC are more closely related to each other and to the mouse Msx3. Similarly, although the combinatorial expression of the zebrafish msx genes in the embryonic dorsal neuroectoderm, visceral arches, fins, and sensory organs suggests functional similarities with the Msx genes of other vertebrates, differences in the expression patterns preclude precise assignment of orthological relationships. Distinct duplication events may have given rise to the msx genes of modern fish and other vertebrate lineages whereas many aspects of msx gene functions during embryonic development have been preserved.      

Möglichkeiten der Gewinnung von Koppelprodukten der mikrobiellen Eiweißsynthese auf der Basis von Kohlenwasserstoffen

The mass production of SCP on the base of hydrocarbons opens the possibility to get a complex of further substances. It is distinguished between by-products – belonging to essential nonprotein – structures of the growing cell and the so – called coupled products accumulating intra – or extracellularly by means of regulation. An important principle of SCP-coupled synthesis of products is the use and the maintenance of proportionality between the growth rate and cell concentration of the producing cells and the accumulation of products. As examples are discussed: fermentation by yeasts and bacteria on the base of n-alkanes, methane and methanol in connection with products as fatty acids, poly-β-hydroxybutyric acid, citric and gluconic acid.     

Surface structure changes of rat adipocytes during lypolysis stimulated by various lypolysis stimulated by various lypolytic agents

A qualitative and quantitative electron microscopic study was performed on rat adipocytes during stimulation of lipolysis by various agents. Scanning electron microscopy of control cells revealed a spherical cell with a textured glycocalyx surface exhibiting small irregular projections. Globular surface evaginations or protrusions measuring 8-18 μM in diameter were seen on cell hemispheres, and there was an average of one protrusion for every two hemispheres examined. Distribution analysis showed that 60 percent of the hemispheres had no protrusions, and 25, 10, and 5 percent of the hemispheres had one, two or three protrusions, respectively. Thin-section and freeze- fracture electron microscopy of the protrusions showed a small triglyceride droplet surrounded by a thin cytoplasmic rim that was continuous with the main cytoplasmic matrix. The glycocalyx coating and plasma membrane extended from the cell surface onto, and over, the protrusion. Scanning microscopy of cells stimulated by lipolytic agents, including epinephrine, adrenocorticotropic hormone, theophylline, and dibutyryl cyclic AMP, revealed a dose-dependent increase in the number of protrusions per cell hemisphere. Maximal concentrations of lipolytic hormones cuase an average 2.5-fold increase in the number of protrusions per hemisphere without changing the average size of the protrusions. Only 40 percent of the stimulated cell hemispheres exhibited no protrusions; over 15 percent of the cells contained three or more; and a number of the protrusions were multilobulate. Insulin prevented the increase in the number of protrusions and the change in distribution caused by the lipolytic hormones but did not prevent the increase caused by theophylline and dibutryl cyclic AMP. The data suggest that the protrusions are a structural feature of the cell and may be related to the lypolytic pathway. These observations may help explain some of the discrepant biochemical data relating to hormonal stimulation of lipolysis.     

PERIANTH DEVELOPMENT OF POTAMOGETON RICHARDSONII

Interpretation of the Potamogeton flower is complicated by the attachment of the “perianth segment” to the stamen connective. Developmental studies show that the perianth segments are not outgrowths of the stamen connectives. They are initiated on the floral apex acropetally before the (superposed) primordia of the stamens. After the inception of the stamen primordia, growth occurs in the regions between the primordia of each perianth segment and stamen. Thereby the bases of the developing perianth segment and stamen become united, and in the adult flower eventually the perianth segment is inserted on the connective of the stamen. The primordium of the perianth segment develops from the 2 outer layers (tunica) of the floral apex, in contrast to the stamen primordium which originates from the 3 outer layers. The vascular bundles for each perianth segment–stamen region develop acropetally from 1 common bundle which bifurcates into 1 bundle for the perianth segment and 1 for the stamen. The bundle leading into the perianth segment branches in a more or less dichotomous manner. The veins form none or only 1 or 2 anastomoses at the base of the lamina, whereas the vein endings remain free. The interpretation of the perianth segments is discussed in terms of the classical and the gonophyll theory. Since both theories rest on an ambiguous methodological basis, interpretation is postponed until a new approach to comparative morphology has been worked out and until the floral development of other Helobiales has been studied.     

Highly divergent methyltransferases catalyze a conserved reaction in tocopherol and plastoquinone synthesis in cyanobacteria and photosynthetic eukaryotes

Tocopherols are lipid-soluble compounds synthesized only by photosynthetic eukaryotes and oxygenic cyanobacteria. The pathway and enzymes for tocopherol synthesis are homologous in cyanobacteria and plants except for 2-methyl-6-phytyl-1,4-benzoquinone/2-methyl-6-solanyl-1,4-benzoquinone methyltransferase (MPBQ/MSBQ MT), which catalyzes a key methylation step in both tocopherol and plastoquinone (PQ) synthesis. Using a combined genomic, genetic, and biochemical approach, we isolated and characterized the VTE3 (vitamin E defective) locus, which encodes MPBQ/MSBQ MT in Arabidopsis. The phenotypes of vte3 mutants are consistent with the disruption of MPBQ/MSBQ MT activity to varying extents. The ethyl methanesulfonate-derived vte3-1 allele alters tocopherol composition but has little impact on PQ levels, whereas the null vte3-2 allele is deficient in PQ and alpha- and gamma-tocopherols. In vitro enzyme assays confirmed that VTE3 is the plant functional equivalent of the previously characterized MPBQ/MSBQ MT (Sll0418) from Synechocystis sp PCC6803, although the two proteins are highly divergent in primary sequence. Sll0418 orthologs are present in all fully sequenced cyanobacterial genomes, Chlamydomonas reinhardtii, and the diatom Thalassiosira pseudonana but absent from vascular and nonvascular plant databases. VTE3 orthologs are present in all vascular and nonvascular plant databases and in C. reinhardtii but absent from cyanobacterial genomes. Intriguingly, the only prokaryotic genomes that contain VTE3-like sequences are those of two species of archea, suggesting that, in contrast to all other enzymes of the plant tocopherol pathway, the evolutionary origin of VTE3 may have been archeal rather than cyanobacterial. In vivo analyses of vte3 mutants and the corresponding homozygous Synechocystis sp PCC6803 sll0418::aphII mutant revealed important differences in enzyme redundancy, the regulation of tocopherol synthesis, and the integration of tocopherol and PQ biosynthesis in cyanobacteria and plants.