Adduct formation between sulfite and the flavin of phototrophic bacterial flavocytochromes c. Kinetics of sequential bleach, recolor, and rebleach of flavin as a function of pH.

The kinetics of sulfite adduct formation with the bound flavin in flavocytochromes c from the purple phototrophic bacterium Chromatium vinosum and the green phototrophic bacterium Chlorobium thiosulfatophilum have been investigated as a function of pH. Both species of flavocytochrome c rapidly react with sulfite to form a flavin sulfite adduct (k = 10(3)-10(5) M-1 s-1) which is bleached at 450-475 nm and has associated charge-transfer absorbance at 660 nm. The rate constant for adduct formation in flavocytochrome c is 2-4 orders of magnitude faster than for model flavins of comparable redox potential and is likely to be due to a basic residue near the N-1 position of the flavin, which not only raises the redox potential but also stabilizes the negatively charged adduct. There is a pK for adduct formation at 6.5, which suggests that the order of magnitude larger rate constant at pH 5 as compared to pH 10 in flavocytochrome c is due the influence of another positive charge, possibly a protonated histidine residue. The adduct is indefinitely stable at pH 5 but decomposes (the flavin recolors) in a first-order process accelerating above pH 6 (at pH 10, k = 0.1 s-1). The pK for recoloring is 8.5, which is suggestive of a cysteine sulfhydryl. On the basis of the observed pK and available chemical information, we believe that recoloring is due to a secondary effect of the reaction of sulfite with a protein cystine disulfide, which is adjacent to the flavin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of canine surfactant protein (SP-A) on the respiratory burst of phagocytic cells

Cells obtained from bronchoalveolar lavage, or neutrophils of peripheral blood of dog, were incubated with the canine surfactant-associated protein A (SP-A). A significant decrease of the production of Superoxide anion was observed after subsequent stimulation with phorbol-12-myristate-13-acetate (PMA) as measured by the lucigenin-dependent chemiluminesence (CL). Several other proteins used for control experiments did not decrease lucigenin-dependent CL, indicating a specific effect of SP-A on phagocytes. Treatment of SP-A with collagenase prior to incubation with neutrophils destroyed the depleting effect on oxygen radical production of PMA-stimulated cells. We propose that SP-A acts as a regulatory factor of the respitatory burst of alveolar macrophages and neutrophils in the lungs. The inhibitory effect of SP-A is down-regulated by collagenase released from stimulated alveolar macrophages.     

Behavioral responses of weakly electric fish to complex impedances

Summary Members of the family of African electric fish, Mormyridae, exhibit a novelty response, consisting of an acceleration in the rate of electric organ discharges (EODs), when faced with changes in feedback arising from their EODs. In this study, the novelty responses of three different species of mormyrids to shunts with different electrical characteristics were noted. The three species differed in the frequency contents of their EODs: two species had relatively high spectral frequencies in their EODs (>10 kHz), while the third species had only lower spectral frequencies (< 10 kHz). Primarily resistive shunts elicited novelty response accelerations in all three species, and the magnitudes of these responses, when normalized to the responses obtained for a shunt with no introduced resistance, were comparable for all three species. For primarily capacitive shunts, however, the magnitudes of the normalized responses were different for the three species: the two species with high spectral frequencies in their EODs showed larger normalized responses than the third species which had only low EOD spectral frequencies.The differences in species responses for capacitive shunts, and the similarities in species responses for resistive shunts, suggest that electric fish detect the complex impedance of objects in their near field environment: a circuit model consisting of a fish emitting discharges into the surrounding water, which can be shunted by a variable complex impedance, conforms well to the data. Thus, electrolocation is a frequency dependent sensory process, and this frequency dependency should be considered in any speculation about the adaptive value of different EOD waveforms.Abbreviation EOD electric organ discharge     

Sequence complexity of poly(A) RNA fromPhysarum polycephalum

Summary Poly(A) RNA from S phase, G₂ phase and starved macroplasmodia of Physarum contain mRNA sequences which when translated in vitro, yield similar patterns of polypeptides after fluorography.Reassociation of nick-translated DNA (Cot) allows the isolation of highly labeled single copy DNA which, after saturation hybridization with poly(A) RNA, gives values of 23% for growth and 17% for starvation.Homologous cDNA/poly(A) RNA hybridization reactions (Rot) indicate that 22–28% of the genome is transcribed during growth and 12% during starvation and that about half of the cDNA reacts with 0.1% of the genome and could represent 50–80 RNA species, each present in about 1,000 copies per nucleus. Up to 25,000 different RNA species, 1–5 copies each per nucleus, are estimated to be present during growth, and about 15,000 during starvation. Heterologous cDNA/poly(A) RNA hybridization reactions (Rot) indicate that the RNA sequences in S and G₂ phase of the cell cycle are similar, with RNA sequences being more abundant in G₂ phase.During starvation about 25% of the sequences present during growth cannot be detected and those sequences present during growth have become diluted during starvation.     

Isolation of an aggregation inhibitory factor from non-adhesive mouse teratoma cells

An aggregation inhibitory factor (AIF) has been extracted from mouse ascites teratoma cells (that do not aggregate in culture) that retards adhesion of cultured teratoma cells of the same cell line (that do aggregate). Preliminary characterization of AIF on polyacrylamide gels suggests that AIF is a protein composed of four subunits. Extraction of AIF from ascites teratoma cells was accomplished without significant loss of viability by a technique involving the application of an electric field to large numbers of whole cells suspended in a hypertonic electrode buffer. In tests of adhesion, AIF consistently and immediately inhibited aggregation of cultured teratoma cells after 5, 10, 15, and 30 min of incubation. Furthermore, a reduced concentration of AIF resulted in a corresponding decrease in inhibition, suggesting a concentration-dependent action. AIF may help explain how cultured teratoma cells adhere, whereas ascites teratoma cells of the same subline do not adhere.     

Use of an IgG fragment prepared with particulate plasmin to study the C1 binding and activation.

Facb, fragment antigen and complement binding (this last property is shown when the fragment is involved in an immune complex); Fc, C-terminal half of the heavy-chain dimer; pFc′, major C-terminal fragment released from IgG by pepsin or plasmin digestion; DFP, diisopropylphosphofluoridate; ATEE, N-acetyl-L-tyrosine ethyl ester; BAEE, N-benzoyl-L-arginine ethyl ester; TAME, p-toluene sulfonyl-L-arginine methyl ester; SDS, sodium dodecyl sulfate; SBTI, soybean trypsin inhibitor.The nomenclature of the complement components (C1, C1q, C1r, C1s) follows the W.H.O. recommendations. Enzymatic activities are expressed in nanokatals (nkat.) as recommended in the Enzyme Nomenclature (1973).