Methyl bromide inhibits ripening and ethylene production in tomato (lycopersicon esculentum mill.) fruit

Tomato fruit ripening and ethylene production were inhibited following treatment with methyl bromide (MB). Methyl bromide significantly delayed ripening initiation in mature-green (MG) fruit and retarded the rate of ripening of turning (T) fruit as measured by color development and flesh softening. Treatment with MB caused an initial transient burst of ethylene production, but the subsequent ripening-associated increase in ethylene was delayed. Ethylene treatment partially overcame MB inhibition in MG fruit but had no affect on T fruit. The inhibition of ethylene production by MB appears to be due to lack of formation of 1-aminocycloprone-1-carboxylic acid (ACC) in MG fruit, whereas in T fruit lack of conversion of ACC to ethylene is indicated. A key feature of MB inhibition of ripening in tomato appears to be reduced sensitivity to ethylene.     

A detailed examination of the iodination of beta-galactosidase: stoichiometric inactivation by nonspecific iodination

The incorporation of 125I, using lactoperoxidase, and the subsequent inactivation of beta-galactosidase in the period when incorporation and inactivation were stoichiometric were investigated in detail. The high pressure liquid chromatographic (HPLC) radioactive profiles of the tryptic peptides of samples taken in the stoichiometric period showed that, although two labelled peptides predominated, there were other labelled peptides. The predominating peptides were shown to be the mono- and di-iodinated forms of the peptide containing Tyr-253. This confirmed the result of an earlier study, but quantitation showed that this iodination accounted for only 15-18% of the total. To show that the other labelled peptides in the HPLC profiles were not merely oxidized or partially digested forms of the peptide containing Tyr-253, two experiments were carried out. In one of the experiments, two of the other labelled peptides were isolated and identified as iodinated forms of the peptide containing Tyr-285 (5-7% of the incorporation). In the other experiment, four additional labelled fractions from the HPLC eluate were treated further with trypsin. No further digestion was observed and thus these peptides did not result from incomplete digestion of the sequence containing Tyr-253. Overall, these results show that, although the incorporation of 125I was stoichiometric with inactivation, no single Tyr was responsible for the inactivation as was tentatively suggested previously. The competitive inhibitor isopropyl-beta-D-thiogalactopyranoside (IPTG) was effective in reducing the rates of inactivation of the enzyme and incorporation of 125I, but the same peptides were labelled in the presence of IPTG as in its absence.     

Changes in Starch Formation and Activities of Sucrose Phosphate Synthase and Cytoplasmic Fructose-1,6-bisphosphatase in Response to Source-Sink Alterations

Short term experiments were conducted with vegetative soybean plants (Glycine max L. Merr. `Ransom' or `Arksoy') to determine whether sourcesink manipulations, which rapidly changed the `demand' for sucrose and partitioning of photosynthetically fixed carbon into starch, were associated with alterations in activities of sucrose-P synthase and/or cytoplasmic fructose-1,6-bisphosphatase in leaf extracts. When demand for sucrose from a particular source leaf was increased by defoliation of other source leaves, starch accumulation was restricted and activities of both enzymes were markedly enhanced. When demand for sucrose from source leaves was limited by excision, starch accumulation in the detached leaves was increased while activity of sucrose-P synthase declined sharply. The consistent responsiveness of sucrose-P synthase activity to changes in demand for sucrose supports the contention that regulation of sucrose-P synthase is an integral component of the system which controls sucrose biosynthesis and partitioning of carbon between starch and sucrose biosynthesis in the light.     

Enzyme des Stärkeumsatzes in Bündelscheiden- und Palisadenchloroplasten von Zea mays

Summary Isolated chloroplasts from the bundle sheath cells show considerable activity of the ADPG- and UDPG-pyrophosphorylase (EC 2.7.7.9), ADPG- and UDPG-transglucosylase (EC 2.4.1.21), and the starch phosphorylase (EC 2.4.1.1). In chloroplasts of the palisade cells, on the other hand, only the UDPG-pyrophosphorylase is remarkably active.     

Crystal structure of plakalbumin, a proteolytically nicked form of ovalbumin. Its relationship to the structure of cleaved alpha-1-proteinase inhibitor

The crystal structure of plakalbumin, a proteolytically nicked form of ovalbumin, has been determined to a resolution of 2.8 A by the isomorphous replacement method and preliminary refinement. The structure closely resembles that of the cleaved form of alpha-1-proteinase inhibitor, with some important exceptions. The disposition of the new carboxyl chain terminus liberated by proteolysis is different with respect to the central beta-sheet A in the structures of these two molecules. In alpha-1-proteinase inhibitor, the new chain terminus inserts in beta-sheet A to add a middle strand to the sheet. In plakalbumin, this strand remains free near the site at which the cleavage occurs. A structural basis for this difference in behavior is proposed from the structures and sequences of these two molecules and other members of the serpin family. The structures and positions of the putative signal peptide of ovalbumin, the several post-translational modifications, and the relationship of the intron-exon patterns of plakalbumin and alpha-1-proteinase inhibitor to their protein structures are also described.     

Crystals of the NC1 domain of human type IV collagen

Crystals of the non-collagenous C-terminal region (NC1) of type IV collagen have been obtained from human placenta. These crystals diffract to 2.0 A, and belong to space group P22(1)2(1), with cell dimensions a = 81 A, b = 158 A, c = 138 A, alpha = beta = gamma = 90 degrees. The crystals contain one hexamer in the asymmetric unit; they are very stable with respect to X-rays.     

Refined three-dimensional structure of phycoerythrocyanin from the cyanobacterium Mastigocladus laminosus at 2.7 A

The structure of the phycobiliprotein phycoerythrocyanin from the thermophilic cyanobacterium Mastigocladus laminosus has been determined at 2.7 A resolution by X-ray diffraction methods on the basis of the molecular model of C-phycocyanin from the same organism. Hexagonal phycoerythrocyanin crystals of space group P6(3) with cell constants a = b = 156.86 A, c = 40.39 A, alpha = beta = 90 degrees, gamma = 120 degrees are almost isomorphous to C-phycocyanin crystals. The crystal structure has been refined by energy-restrained crystallographic refinement and model building. The conventional crystallographic R-factor of the final model was 19.2% with data to 2.7 A resolution. In phycoerythrocyanin, the three (alpha beta)-subunits are arranged around a 3-fold symmetry axis, as in C-phycocyanin. The two structures are very similar. After superposition, the 162 C alpha atoms of the alpha-subunit have a mean difference of 0.71 A and the 171 C alpha atoms of the beta-subunit differ by 0.51 A. The stereochemistry of the chiral atoms in the phycobiliviolin chromophore A84 is C(31)-R, C(4)-S. The configuration of the chromophore is C(10)-Z, C(15)-Z and the conformation C(5)-anti, C(9)-syn and C(14)-anti like the phycocyanobilin chromophores in phycoerythrocyanin and C-phycocyanin.     

Crystallization and preliminary X-ray studies of the VL domain of the antibody McPC603 produced in Escherichia coli

The VL domain, obtained from a recombinant Fv fragment of the antibody McPC603 expressed in Escherichia coli, has been crystallized as a dimer from 2 M-(NH4)2SO4 (pH 4.0). The crystals are hexagonal, space group P6(1)22. The cell dimensions are a = b = 86.48 A, c = 76.64 A, with a VL monomer as the asymmetric unit. The crystals diffract to 2.0 A. The structure was solved by Patterson search using the VL domain of the Fab fragment of McPC603 and the VL dimer REI.