Interaction of alcohol and protein deficiency on rat brain synaptosomal (Na+−K+)-ATPase

Administration of low amounts of ethanol for a prolonged period increases rat brain synaptosomal (Na⁺–K⁺)-ATPase activity, the increase being less in the protein deficient rats. The adaptive mechanism to offset the stress imposed by the continued presence of ethanol seems to be depressed by low plane of nutrition. In vivo and in vitro effects of ethanol on (Na⁺–K⁺)ATPase seems to be different.     

Temporal relationship between nerve-stump-length-dependent changes in the autophosphorylation of a cyclic AMP-dependent protein kinase and the acetylcholine receptor content in skeletal muscle

The acetylcholine receptor (AChR) content and the autorphosphorylation of the regulatory subunit of cyclic AMP-dependent protein kinase type II (R-II) were evaluated in rat soleus muscles at 24, 30 and 66 hr after surgical denervation by cutting the nerve at a short distance (short-nerve-stump) and at a long distance (long-nerve-stump) from the muscle. AChR content was based on the specific binding of [¹²⁵I]alpha-bungarotoxin (BUTX); changes in the autophosphorylation of R-II were based upon the predominant in vitro³²P-phosphorylation of a 56-Kd soluble protein in cytosolic fractions of solei. The AChR content and the³²P-autophosphorylation of R-II were increased in samples from short-nerve-stump solei, but not from long-nerve-stump solei, after a denervation-time of 30 hr. This nerve-stump-length dependency indicates that the two denervation effects are not related to the immediate halt of impulse-evoked muscle contractility. Furthermore, the results show that alterations in the³²P-autophosphorylation of R-II occurred before, as well as whenever, increases in the AChR content were found. Speculatively, this temporal relationship may be significant with respect to the potential role of R-II in gene expression.Abbreviations ACh acetylcholine - AChR acetylcholine receptor(s) - BUTX alpha-bungarotoxin - Kd kilodalton - PAGE polyacrylamide gel electrophoresis - R-II regulatory subunit of cyclic AMP-dependent protein kinase type II - SDS sodium dodecyl sulfate     

Intergeneric relationships ofLolium,Festuca, andVulpia (Poaceae) and their phylogeny

Morphological and seed protein analyses of 26 species of the generaLolium, Festuca andVulpia confirmed their close systematic affinities. Six inflorescence characters readily differentiatedFestuca fromLolium. Protein similarities betweenFestuca of sect.Bovinae and cross-pollinated species ofLolium, coupled with cytogenetic and crossability data, substantiate that they should be united into one genus.Vulpia had phenetic similarities with sect.Scariosae, Montanae andOvinae ofFestuca. Lolium, Festuca, andVulpia are most likely derived from a common ancestral form which was close toFestuca pratensis andLolium perenne.     

Amino acid identities in the three redox center-carrying polypeptides of cytochromebc 1/b 6 f complexes

The comparison of primary structures is extended to 22 cytochromesb orb ₆, 12 cytochromesc ₁ orf, and 8 Rieske FeS proteins. Conclusions are drawn as to their phylogenetic relationship as well as on conserved, functionally important amino acids and secondary structures. The results are in favor of two independent quinone binding sites at opposite surfaces of the membrane, topping one of the two hemes of cytochromeb each.     

Complexity and tissue specificity of the mitochondrial respiratory chain

There is a renewed interest in the structure and functioning of the mitochondrial respiratory chain with the realization that a number of genetic disorders result from defects in mitochondrial electron transfer. These so-called mitochondrial myopathies include diseases of muscle, heart, and brain. The respiratory chain can be fractionated into four large multipeptide complexes, an NADH ubiquinone reductase (complex I), succinate ubiquinone reductase (complex II), ubiquinol oxidoreductase (complex III), and cytochromec oxidase (complex IV). Mitochondrial myopathies involving each of these complexes have been described. This review summarizes compositional and structural data on the respiratory chain proteins and describes the arrangement of these complexes in the mitochondrial inner membrane. This biochemical information is provided as a framework for the diagnosis and molecular characterization of mitochondrial diseases.     

Characteristics of human milk glutathione peroxidase

Human milk glutathione peroxidase (GPx) was purified 4500-fold using acetone precipitation and purification by repetitive ion-exchange and gel filtration chromatography with an overall yield of 34%. Homogeneity was established by gel electrophoresis. Using gel filtration, the molecular weight (mol wt) of the enzyme was estimated to be 92 kdalton (kD). The monomeric molecular weight was estimated to b 23 kD from polyacrylamide gel electrophoresis, indicating that the native enzyme consists of four identical subunits. The molecular weight of each subunit was supported by amino acid analysis. Selenium (Se) content of the purified enzyme was 0.31%, in a stoichiometry of 3.7 g-atoms/mol. Data from these studies reveal that GPx provided approximately 22% of total milk Se, but only 0.025% of the total protein.     

Recent developments in chloroplast protein transport

Most proteins located in chloroplasts are encoded by nuclear genes, synthesized in the cytoplasm, and transported into the organelle. The study of protein uptake by chloroplasts has greatly expanded over the past few years. The increased activity in this field is due, in part, to the application of recombinant DNA methodology to the analysis of protein translocation. Added interest has also been gained by the realization that the transport mechanisms that mediate protein uptake by chloroplasts, mitochondria and the endoplasmic reticulum display certain characteristics in common. These include amino terminal sequences that target proteins to particular organelles, a transport process that is mechanistically independent from the events of translation, and an ATP-requiring transport step that is thought to involve partial unfolding of the protein to be translocated. In this review we examine recent studies on the binding of precursors to the chloroplast surface, the energy-dependent uptake of proteins into the stroma, and the targeting of proteins to the thylakoid lumen. These aspects of protein transport into chloroplasts are discussed in the context of recent studies on protein uptake by mitochondria.Abbrevlations CAT chloramphenicol acetyl transferase - CCCP carbonylcyanide m-chlorophenylhydrazone - DHFR dihydrofolate reductase - EPSP 5-enol-pyruvylshikimate-3-phosphate - ER endoplasmic reticulum - LHCP light harvesting chlorophyll a/b apoprotein - NPT neomycin phosphotransferase - oATP adenosine-2,3-dialdehyde-5-triphosphate - P-inorganic phosphate Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - SSU small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase - SRP signal recognition particle     

Synthesis and assembly of the cytochrome b-f complex in higher plants

The cytochrome b-f complex is composed of four polypeptide subunits, three of which, cytochrome f, cytochrome b-563 and subunit IV, are encoded in chloroplast DNA and synthesised within the chloroplast, and the fourth, the Rieske FeS protein, is encoded in nuclear DNA and synthesised in the cytoplasm. The assembly of the cytochrome b-f complex therefore requires the interaction of subunits encoded by different genomes. A key role for the nuclear-encoded Rieske FeS protein in the assembly of the complex is suggested by a study of cytochrome b-f complex mutants. The assembly of individual subunits of the complex may be regulated by the availability of prosthetic groups. The genes for the chloroplast-encoded subunits and cDNA clones for the Rieske FeS protein have been isolated and characterised. Cytochrome f and the Rieske FeS protein are synthesised initially with N-terminal presequences required for their correct assembly within the chloroplast. The deduced amino acid sequences of the four subunits have been used to suggest models for the arrangement of the polypeptides in the thylakoid membrane.     

Molecular characterization of the virulence gene virA of the Agrobacterium tumefaciens octopine Ti plasmid

The virulence loci play an essential role in tumor formation by Agrobacterium tumefaciens. Induction of vir gene expression by plant signal molecules is solely dependent on the virulence loci virA and virG. This study focused on the virA locus of the octopine type Ti plasmid pTi15955. The nucleic acid sequence of a 5.7-kilobase fragment encompassing virA was determined. Genetic analysis of this region revealed that virA contains one open reading frame coding for a protein of 91 639 daltons. Immunodetection with antibodies raised against a 35-kDa VirA fusion protein produced in E. coli identified the VirA product in wild-type Agrobacterium cells. Moreover, it is shown that the VirA protein is located in the cytoplasmic membrane fraction of Agrobacterium. These data confirm the proposed regulatory function of VirA whereby VirA acts as a membrane sensor protein to identify plant signal molecules in the environment. The proposed sensory function of VirA strikingly resembles the function of the chemotaxis receptor proteins of E. coli.