The role of vanadium in green plants

Cells of Chlorella pyrenoidosa, derived from vanadium free agar slants, respond with great sensitivity to microamounts of vanadium, added as NH₄VO₃ to autotrophic liquid cultures. Between 0.01 and 1 g V per litre nutrient medium (2·10^-10-2·10^-8g-at/l), the algae respond with a continuous increase in dry weight. At higher V-concentrations, further enhancement in biomass is accompanied by a additional increase in chlorophyll content. Maximum V-effect on both parameters was found to be at 500g V/l (10^-5 g-at/l). Dry weight as well as chlorophyll content of Chlorella are decreased by concentrations above 25 mg V/l; 100 mg V/l (2·10^-3 g-at/l) stop growth and cause death of the cells. The toxic threshold for the V-content in the algae was determined to be at 150–200 g V/g (3–4·10^-6 g-at/g) dry weight.Two different pH-optima for a positive vanadium action on dry weight and chlorophyll biosynthesis were established, the first at pH 7, the other in the range pH 7.5–8. Two sites of vanadium action in green algae are discussed.Part I: Arch. Microbiol. 105, 77–82 (1975)     

Psoralen/UVA treatment and chromosomes

Summary Treatment of human lymphocytes in vitro with trimethylpsoralen or 8-methoxypsoralen and UVA irradiation (PUVA) induced chromosome damage, mainly constrictions and gaps, but also breaks and exchanges, and increased the frequency of sister chromatid exchange (SCE). The localization of the chromosome aberrations was nonrandom. The coincidence of many PUVA hits with mercaptoenthanol hits suggests that PUVA may have other targets in the cell than the DNA, perhaps the folding proteins of the chromosomes and the nuclear membrane/chromatin attachment organelles.Caffeine increased in a synergistic way the chromosome aberration yield if added after PUVA treatment, but there was no effect when caffeine was present before and during PUVA treatment. The SCE frequency was increased in the presence of caffeine.     

Density distribution of 2′,3′-cyclic nucleotide 3′-phosphodiesterase and myelin proteins in particulate material from myelin deficient (mld) mutant and control brains

Total particulate material from control and myelin deficient (mld) brains was subjected to density centrifugation on a continuous sucrose gradient. Particles from control brains distributed in a bell-shaped mode with a peak density near 0.64 M-sucrose. In mld material only a slight elevation of optical density was observed near 0.8 M-sucrose. The highest specific activities of 2′,3′-cyclic nucleotide 3′-phosphodiesterase were observed at densities of 0.63 and 0.71 M-sucrose for mld and control brains, respectively. The peak of myelin basic protein in control fractions was near 0.60 M-sucrose. In mld fractions no peak was observed. Proteolipid and Wolfgram proteins had a maximum near 0.65 and 0.73 M-sucrose in control and mld fractions, respectively. The absence of myelin basic proteins in all the fractions makes it unlikely that, in mld mice, myelin basic proteins are synthesized but not incorporated into myelin.     

Distribution of lipid synthesizing enzymes, 2′,3′-cyclic nucleotide 3′-phosphodiesterase,and myelin proteins in rat forebrain subfractions during development

The distribution of UDP-galactose: ceramide galactosyltransferase (CGalT) was studied in subcellular fractions of rat forebrain during development using zonal centrifugation on linear gradients. Specialized subfractions: SN 1, a microsomal fraction, SN 4, a myelin-related fraction, and purified myelin were also used for this study. For comparison, two microsomal lipid synthesizing enzymes, a myelin-specific enzyme, 2,3-cyclic nucleotide 3-phosphodiesterase and myelin proteins were measured in the same subfractions. UDP-glucose: ceramide glucosyltransferase and cerebroside sulfotransferase were confined to microsomes. CGalT was ferase and cerebroside sulfotransferase were confined to microsomes. CGalT was localized in microsomes, but also in myelin and myelin-related fractions. The developmental change in distribution of CGalT in adult animals toward myelin containing fractions could indicate that the replacement of galactosylceramide in compact myelin could be carried out in close proximity to compact myelin (mesaxon, paranodal loops) rather than in the distant oligodendrocyte perikaryon.     

The involvement of phytochrome in controlling chlorophyll and 5-aminolevulinate formation in a gymnosperm seedling (Pinus sylvestris)

Chlorophyll a (Chl a) accumulation in the cotyledons of Scots pine seedlings (Pinus sylvestris L.) is much higher in the light than in darkness where it ceases 6 days after germination. When these darkgrown seedlings are treated with continuous white light (3,500 lx) a 3 h lag phase appears before Chl a accumulation is resumed. The lag phase can be eliminated by pretreating the seedlings with 7 h of weak red light (0.14 Wm^-2) or with 14 red light pulses separated by relatively short dark periods (<100 min). The effect of 15s red light pulses can be fully reversed by 1 min far-red light pulses. This reversibility is lost within 2 min. In addition, the amount of Chl a formed within 27 h of continuous red light is considerably reduced by the simultaneous application of far-red (RG 9) light. It is concluded that phytochrome (P_fr) is required not only for the elimination of the lagphase but also to maintain a high rate of Chl a accumulation in continuous light. Since accumulation of 5-aminolevulinate (ALA) responds in the same manner as Chl a accumulation to a red light pretreatment it is further concluded that ALA formation is the point where phytochrome regulates Chl biosynthesis in continuous light. No correlation has been found between ALA and Chl a formation in darkness. This indicates that in a darkgrown pine seedling ALA formation is not rate limiting for Chl a accumulation.Abbreviations Chl chlorophyll(ide) - PChl protochlorophyll(ide) - ALA 5-aminolevulinate - P_r the red absorbing form of phytochrome - P_fr the far-red absorbing form of phytochrome - P_tot total phytochrome ([P_r]+[P_fr])     

Intracellular concentrations of phenylalanine,tyrosine and α-aminobutyric acid in 13 homozybotes and 19 heterozygotes for phenylketonuria (PKU) compared with 26 normals

Summary Intracellular concentrations of phenylalanine, tyrosine, -aminobutyric acid, and seven other aminoacids (glycine, alanine, valine, cystine, methionine, isoleucine, leucine) were measured in lymphocytes of 13 homozygotes and 19 heterozygotes for phenylketonuria and in lymphocytes of 26 normals. Intracellular concentrations for phenylalanine, tyrosine, and -aminobutyric acid were significantly higher in homo- and heterozygotes than in normals (P<0.001; P<0.01). For the other seven aminoacids there were no or only questionable differences. Between homo-and heterozygotes there was no difference in any of the aminoacids. The intracellular phenylalanine: tyrosine ratio was essentially the same in all three groups of individuals. There was no correlation between intracellular phenylalanine above or below 10nmol/10⁶ cells and IQ in heterozygotes. The same is true for phenylalanine: tyrosine ratio greater or smaller than 1. In homozygotes there was no correlation between intracellular phenylalanine and age—to which DQ/IQ is correlated. There was no significant difference in intracellular phenylalanine between homozygotes with blood levels above and below 908 mol/l (15 mg/100 ml) at the time of blood sampling and no correlation between intra- and extracellular phenylalanine concentrations.Among the 26 normals there were only two with intracellular phenylalanine above 10 nmol/10⁶ cells, both showing phenylalanine loading test curves suggestive of heterozygosity.The results are discussed and important functions of the cell wall are proposed. The formation of an abnormal unknown intracellular metabolite being the real noxious agent could explain the incomparably different degrees of brain dysfunction in individuals with equal though elevated intracellular phenylalanine concentrations, i.e., homozygotes and heterozygotes for PKU.     

Exploring molecular and mechanical gradients in structural bioscaffolds

Most organisms consist of a functionally adaptive assemblage of hard and soft tissues. Despite the obvious advantages of reinforcing soft protoplasm with a hard scaffold, such composites can lead to tremendous mechanical stresses where the two meet. Although little is known about how nature relieves these stresses, it is generally agreed that fundamental insights about molecular adaptation at hard/soft interfaces could profoundly influence how we think about biomaterials. Based on two noncellular tissues, mussel byssus and polychaete jaws, recent studies suggest that one natural strategy to minimize interfacial stresses between adjoining stiff and soft tissue appears to be the creation of a "fuzzy" boundary, which avoids abrupt changes in mechanical properties. Instead there is a gradual mechanical change that accompanies the transcendence from stiff to soft and vice versa. In byssal threads, the biochemical medium for achieving such a gradual mechanical change involves the elegant use of collagen-based self-assembling block copolymers. There are three distinct diblock copolymer types in which one block is always collagenous, whereas the other can be either elastin-like (soft), amorphous polyglycine (intermediate), or silk-like (stiff). Gradients of these are made by an incrementally titrated expression of the three proteins in secretory cells the titration phenotype of which is linked to their location. Thus, reflecting exactly the composition of each thread, the distal cells secrete primarily the silk- and polyglycine-collagen diblocks, whereas the proximal cells secrete the elastin- and polyglycine-collagen diblocks. Those cells in between exhibit gradations of collagens with silk or elastin blocks. Spontaneous self-assembly appears to be by pH triggered metal binding by histidine (HIS)-rich sequences at both the amino and carboxy termini of the diblocks. In the polychaete jaws, HIS-rich sequences are expanded into a major block domain. Histidine predominates at over 20 mol % near the distal tip and diminishes to about 5 mol % near the proximal base. The abundance of histidine is directly correlated to transition metal content (Zn or Cu) as well as hardness determined by nanoindentation. EXAFS analyses of the jaws indicate that transition metals such as Zn are directly bound to histidine ligands and may serve as cross-linkers.     

Signal peptide hydrophobicity is critical for early stages in protein export by Bacillus subtilis

Signal peptides that direct protein export in Bacillus subtilis are overall more hydrophobic than signal peptides in Escherichia coli. To study the importance of signal peptide hydrophobicity for protein export in both organisms, the alpha-amylase AmyQ was provided with leucine-rich (high hydrophobicity) or alanine-rich (low hydrophobicity) signal peptides. AmyQ export was most efficiently directed by the authentic signal peptide, both in E. coli and B. subtilis. The leucine-rich signal peptide directed AmyQ export less efficiently in both organisms, as judged from pulse-chase labelling experiments. Remarkably, the alanine-rich signal peptide was functional in protein translocation only in E. coli. Cross-linking of in vitro synthesized ribosome nascent chain complexes (RNCs) to cytoplasmic proteins showed that signal peptide hydrophobicity is a critical determinant for signal peptide binding to the Ffh component of the signal recognition particle (SRP) or to trigger factor, not only in E. coli, but also in B. subtilis. The results show that B. subtilis SRP can discriminate between signal peptides with relatively high hydrophobicities. Interestingly, the B. subtilis protein export machinery seems to be poorly adapted to handle alanine-rich signal peptides with a low hydrophobicity. Thus, signal peptide hydrophobicity appears to be more critical for the efficiency of early stages in protein export in B. subtilis than in E. coli.