Reversible steps in the reaction of aldehydes with bacterial luciferase intermediates.

Aliphatic aldehydes of different chain lengths were found to differ in their reaction at 22 °C with the B. harveyi luciferase peroxyflavin intermediate. Although similar quantum yields were obtained in the luciferase reaction with the different chain-length aldehydes, the catalytic turnover rates differed. The kinetics of a reaction utilizing two aldehydes of different chain lengths can thus indicate the degree to which the aldehyde reaction is reversible. By such criteria the reactions of octanal and decanal were found to be readily reversible, while that of dodecanal was not. This conclusion was supported both by the effects of long-chain alcohols, which are competitive inhibitors, and by the secondary addition of hydroxylamine, an aldehyde trapping agent. The results are consistent with a model in which there are many intermediates along the reaction path. Since the reactions are monitored by decay of luminescence intensity, it is difficult to determine the position of the rate-determining step. For octanal and decanal the rate-limiting step could be at an early reversible stage of the reaction, but later for dodecanal, subsequent to a less reversible step, but still prior to the final irreversible step which populates the excited state.     

The Role of Gravity in Apical Dominance : Effects of Clinostating on Shoot Inversion-Induced Ethylene Production, Shoot Elongation, and Lateral Bud Growth

Shoot inversion-induced release of apical dominance in Pharbitis nil is inhibited by rotating the plant at 0.42 revolutions per minute in a vertical plane perpendicular to the axis of rotation of a horizontal clinostat. Clinostating prevented lateral bud outgrowth, apparently by negating the restriction of the shoot elongation via reduction of ethylene production in the inverted shoot. Radial stem expansion was also decreased. Data from experiments with intact tissue and isolated segments indicated that shoot-inversion stimulates ethylene production by increasing the activity of 1-aminocyclopropane-1-carboxylic acid synthase. The results support the hypothesis that shoot inversion-induced release of apical dominance in Pharbitis nil is due to gravity stress and is mediated by ethylene-induced retardation of the elongation of the inverted shoot.     

Functional Changes Associated with Structural Alterations Induced by Mobilization of a P Element Inserted in the Sex-lethal Gene of Drosophila

Genetic analysis of rearrangements within the multifunctional sex determining gene Sex-lethal has allowed correlation of changes in specific functions with DNA alterations. Rearrangements were isolated by mobilization of a P element which is on the 5' side of the gene, at coordinate 0. Previous work has shown that rearrangements associated with alterations in Sxl gene function are found within an 11-kb region between coordinates-11 and 0. Here it is shown that insertion of foreign DNA, per se, at coordinate 0 is compatible with wild-type gene function. However, deletion of sequences on either side of this point generates a mutant phenotype. Deletions extending distally beyond coordinate -6.5 kb result in a null phenotype, whereas smaller distal deletions or proximal deletions eliminate only some Sxl functions.     

Alterations of class I HLA genes in human colon cancers

Summary Alterations of HLA class I genes were found in 3 of 12 human colon cancers. Rearrangements in HLA class I genes were observed in 2 cancers and amplification of HLA-coding genes was observed in 1 cancer. All 3 cancers were at an advanced stage. No examples of amplification or rearrangement in the HLA genes were found in 10 other tumours of diverse types. No alterations in the ₂-microgubulin gene were observed in 22 human solid tumours included in this study. The association between alterations in HLA genes and proto-oncogenes in these tumours is discussed.     

The effects of low levels of chloramphenicol and methotrexate on somatic embryogenesis inCitrus

Summary The effects of the antibiotics methotrexate and chloramphenicol on somatic embryogenesis inCitrus were evaluated. Relatively low levels (0.1 to 1.0 μg/ml) of these antibiotics did not inhibit embryo production from undeveloped ovules of ‘Key’ lime [C. aurantifolia) (Christm.) Swing.]. Surprisingly, both antibiotics induced the formation of embryogenic callus in these cultures. This is usually a rare event in cultures of undevelopedCitrus ovules, and ‘Key’ lime is especially recalcitrant. The effects of these antibiotics on embryogenic callus appeared to be limited to the induction stage, because there was no consistent effect, either stimulatory or inhibitory, on established, lines of embryogenic callus. Florida Agricultural Experiment Station Journal Series No. 8958. This research was supported in part by a grant to Moore and Cline from the Competitive Grants Office of the SEA, USDA (85-CRCR-1-1623).     

57Fe and 1H electron-nuclear double resonance of three doubly reduced states Escherichia coli sulfite reductase

We have employed electron-nuclear double resonance (ENDOR) spectroscopy to study the 57Fe hyperfine interactions in the bridged-siroheme [4Fe-4S] cluster that forms the catalytically active center of the two-electron-reduced hemoprotein subunit of Escherichia coli NADPH-sulfite reductase (SiR2-). Previous electron paramagnetic resonance (EPR) and M?ssbauer studies have shown that this enzyme oxidation state can exist in three distinct spectroscopic forms: (1) a "g = 2.29" EPR species that predominates in unligated SiR2-, in which the siroheme Fe2+ is believed to be in an S = 1 state; (2) a "g = 4.88" type of EPR species that predominates in SiR2- in the presence of small amounts of guanidinium sulfate, in which the siroheme Fe2+ is in an S = 2 state; and (3) a classical "g = 1.94" type of EPR species that is seen in SiR2- ligated with CO, in which the siroheme Fe2+ is in an S = 0 state. In all three species, the cluster is in the [4Fe-4S]1+ state, and two distinct types of Fe site are seen in M?ssbauer spectroscopy. ENDOR studies confirm the M?ssbauer assignments for the cluster 57Fe in the g = 1.94 state, with A values of 37, 37, and 32 MHz for site I and ca. 19 MHz for site II. The hyperfine interactions are not too different on the g = 2.29 state, with site I Fe showing more anisotropic A values of 32, 24, and 20 MHz (site II was not detected).(ABSTRACT TRUNCATED AT 250 WORDS)