Photosystem I electron transport and phosphorylation supported by electron donation to the plastoquinone region

In chloroplasts, tetramethyl-p-hydroquinone supports high rates of phosphorylation-coupled, noncyclic electron flow through Photosystem I to methylviologen. The reaction is totally sensitive to dibromothymoquinone, indicating an electron donation to the plastoquinone region of the photosynthetic chain. The uncoupled electron flow rate exceeds 1000 μequivalents per hour per mg chlorophyll. The phosphorylation efficiency ($\text{P}\text{e}{}_2$) at the optimal pH of 8 is 0.6–0.65. Presumably this ratio represents the efficiency of energy coupling in the electron transfer step plastoquinone → cytochrome f.     

An iso-random Bi Bi mechanism for adenylate kinase.

An iso-random Bi Bi mechanism has been proposed for adenylate kinase. In this mechanism, one of the enzyme forms can bind the substrates MgATP and AMP, whereas the other form can bind the products MgADP and ADP. In a catalytic cycle, the conformational changes of the free enzyme and the ternary complexes are the rate-limiting steps. The AP(5)A inhibition equations derived from this mechanism show theoretically that AP(5)A acts as a competitive inhibitor for the forward reaction and a mixed noncompetitive inhibitor for the backward reaction.     

HLA-JY328: Mapping studies and expression of a polymorphic HLA class I gene

The JY328 clone was identified in a human genomic library using cDNA corresponding to mRNA for HLA-B7 as a probe. The L/328 cell line was established by cotransformation of mouse Ltk^– cells with the herpes thymidine kinase gene and clone JY328. On Northern blots, RNA from,L/328 strongly hybridized to an HLA class I probe, and an antigen was recognized by an anti-HLA class I framework antibody on the cell surface. A DNA probe corresponding to a segment of intron 7 was developed by comparing the nucleotide sequence of clone JY328 with that of other HLA class I-type genes. Using the radiolabeled probe to screen Southern blots of DNA from families with siblings exhibiting intra-HLA recombinations, a restriction fragment length polymorphism was revealed —a 1.4 kb BstE II band not present in all individuals. A corresponding fragment was apparent in the base sequence of clone JY328. The occurrence of this band on Southern blots established that JY328 maps distinct from and centromeric to the HLA-C locus and near to the HLA-B locus. Antibody absorption studies and cytotoxicity tests indicated that the JY328 gene product was not an HLA-B antigen but that it did specifically absorb CW7-specific antibody. In sum, these results suggest a novel, polymorphic HLA class I gene which expresses a product serologically similar to HLA-Cw7 but which does not map within the corresponding locus.     

Trace elements in hair of blackfoot disease

Blackfoot disease is a peripheral vascular disease resulting in gangrene of the lower extremities. Though extensive epidemiological study has implicated that high arsenic content in artesian well water of the endemic area, bears some important connection with the disease, the etiology of the disease is still unknown. In this study, attention is paid to multielement determination in order to find out whether the trace elements in hair of Blackfoot disease patients are different from those of the controls. Experimental results indicate that the concentrations of As and Se in hair of patients are significantly higher than those of the controls, but Ca and Zn are significantly lower than those of the controls. The possible connection of these elements with the etiology of the disease is discussed.     

Iron-molybdenum cofactor from nitrogenase. Modified extraction methods as probes for composition

Five modifications of the preparative procedure for isolating iron-molybdenum cofactor (FeMoco) from the molybdenum-iron (MoFe) protein of Azotobacter vinelandii nitrogenase have been developed. This variety of isolation methods has established that no single component of the original isolation protocol, i.e. Tris, Cl-, citrate, HPO4(2-), N,N-dimethylformamide, and N-methylformamide, is essential for the effective isolation and/or structural stability of FeMoco, although any of them may act as ligands to FeMoco when present. The acid-bse status (effective pH) of the extracting solvent is a key adjustable parameter in the isolation procedure. The new procedures produced FeMoco with yields, metal analysis, charge, EPR spectrum, and specific activity (after reconstituting crude extracts from A. vinelandii UW45 mutant cells) essentially identical with FeMoco isolated by the original procedure. After purification, FeMoco apparently contains molybdenum, iron, and sulfide in a 1:7:4 ratio with N-methylformamide as a ligand but no amino acid residues, common sugars, coenzyme A, or lipoic acid. Reaction with o-phenanthroline allows quantitation of both adventitious and FeMoco-associated iron. Correlations of total activity after UW45 reconstitution with molybdenum, total iron, and o-phenanthroline-resistant iron contents show that only the last gives a consistent relationship of 35 +/- 5 nmol of C2H4/min/ng atom of Fe. Both o-phenanthroline and EDTA interact with FeMoco to abolish its EPR signal in reactions reversible by additions of Fe2+ or Zn2+, respectively. These and related reactions point against the presence of an endogenous organic component in FeMoco and toward the presence of exogenous ligands and imply a relatively labile coordination sphere whose nature may be determinable by a systematic investigation.     

Photosystem II energy coupling in chloroplasts with H2O2 as electron donor.

NH2OH-treated, non-water-splitting chloroplasts can oxidize H2O2 to O2 through Photosystem II at substantial rates (100--250 muequiv . h-1 . mg-1 chlorophyll with 5 mM H2O2) using 2,5-dimethyl-p-benzoquinone as an electron acceptor in the presence of the plastoquinone antagonist dibromothymoquinone. This H2O2 leads to Photosystem II leads to dimethylquinone reaction supports phosphorylation with a P/e2 ratio of 0.25--0.35 and proton uptake with H+/e values of 0.67 (pH 8)--0.85 (pH 6). These are close to the P/e2 value of 0.3--0.38 and the H+/e values of 0.7--0.93 found in parallel experiments for the H2O leads to Photosystem II leads to dimethylquinone reaction in untreated chloroplasts. Semi-quantitative data are also presented which show that the donor leads to Photosystem II leads to dibromothymoquinone (leads to O2) reaction can support phosphorylation when the donor used is a proton-releasing reductant (benzidine, catechol) but not when it is a non-proton carrier (I-, ferrocyanide).     

Non‐dormant Axillary Bud 1 regulates axillary bud outgrowth in sorghum

Tillering contributes to grain yield and plant architecture and therefore is an agronomically important trait in sorghum (Sorghum bicolor). Here, we identified and functionally characterized a mutant of the Non‐dormant Axillary Bud 1 (NAB1) gene from an ethyl methanesulfonate‐mutagenized sorghum population. The nab1 mutants have increased tillering and reduced plant height. Map‐based cloning revealed that NAB1 encodes a carotenoid‐cleavage dioxygenase 7 (CCD7) orthologous to rice (Oryza sativa) HIGH‐TILLERING DWARF1/DWARF17 and Arabidopsis thaliana MORE AXILLARY BRANCHING 3. NAB1 is primarily expressed in axillary nodes and tiller bases and NAB1 localizes to chloroplasts. The nab1 mutation causes outgrowth of basal axillary buds; removing these non‐dormant basal axillary buds restored the wild‐type phenotype. The tillering of nab1 plants was completely suppressed by exogenous application of the synthetic strigolactone analog GR24. Moreover, the nab1 plants had no detectable strigolactones and displayed stronger polar auxin transport than wild‐type plants. Finally, RNA‐seq showed that the expression of genes involved in multiple processes, including auxin‐related genes, was significantly altered in nab1. These results suggest that NAB1 functions in strigolactone biosynthesis and the regulation of shoot branching via an interaction with auxin transport.