Adaptations and responses of Dasymutilla occidentalis (Hymenoptera: Mutillidae) to predators

The mutillid wasp Dasymutilla occidentalis possesses several adaptations and exhibits a number of responses wich appear to be of defensive value: a long mobile sting with powerful venom; a strong, rounded and slippery cuticle; an ability to run very rapidly and evasively; an aposematic warning coloration pattern; and the ability to respond to an attack by making stridulatory sounds and by releasing a chemical secretion or both. The effectiveness of these defenses is supported by tests utilizing various vertebrate and arthropod predators. The raison d'être of the multiple lines of defense possessed by D. occidentalis and the relative value of each line of defense are discussed. It is postulated that aposematic coloration, audible stridulation, and a volatile defensive exudate all function primarily as part of an early warning system enabling a predator to recognize this wasp-with its very algogenic venom-as unpalatable and potentially dangerous.

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Zusammenfassung Die Mutillide Wespe Dasymutilla occidentalis besitzt verschiedene Anpassungen und zeigt eine Anzahl von Reaktionen, die für die Verteidigung von Wert sind: ein langer, beweglicher Stachel mit starkem Gift, eine starke, runde und glatte Kutikula, die Möglichkeit, sehr schnell und ausweichend zu laufen sowie ein aposematisches Warn-Farben-Muster. Desweiteren ist sie fähig, einem Angriff mit einem knisternden Ton entgegenzutreten sowie ein chemisches Sekret abzugeben oder auch beides. Im Labor durchgeführte Zusammenstöße zwischen vertebraten und invertebraten Räubern und D. occidentalis beweisen klar den Wert der ganzen Anzahl von Verteidigungsmechanismen für die Wespe.Diese Zusammenstöße liefern auch einen Einblick in die raison d'être der vielseitigen Verteidigung. die stärkere Kutikula und ihre Glätte, Haupteigenschaften zum überleben gegen Räuber, funktionieren gleichzeitig mit dem Stich zum Schutz gegen Vertebraten und mit schneller Fluchtmöglichkeit zum Schutz gegen die meisten Invertebraten. Das akustische Geräusch scheint eine Hilfsverteidigung zu sein wenigstens gegen einige Spinnen und vermutlich auch gegen einige Vertebraten. Die chemische Sekretion, die hauptsächlich aus 4-methyl-3-heptanon besteht, scheint möglicherweise direkten Verteidigungswert gegen einige Eidechsen zu haben und funktioniert höchstwahrscheinlich hauptsächlich im Zusammenhang mit der roten und schwarzen aposematischen Färbung und dem knisternden Ton als vielseitiges Warnsystem, das fähig ist, durch Signalisieren allen potentiellen vertebraten Räubern mitzuteilen, daß dieses Insekt ungenießbar ist.

     

Nuclear magnetic resonance evidence for a structural intermediate at an early stage in the refolding of ribonuclease A

The kinetics of refolding of heat-unfolded ribonuclease A have been studied by Fourier transform proton nuclear magnetic resonance at 10 °C, pH 2. A single refolding reaction is observed: it corresponds to the slow-refolding reaction seen in stopped-flow studies of refolding at higher temperatures. There are two results of interest for the mechanism of protein folding. (1) A new resonance (X) is observed that shows the presence of a structural intermediate in refolding. (2) The α-helix close to the N-terminal end of ribonuclease A apparently forms rapidly when the unfolded protein is brought to refolding conditions.The folding intermediate has been studied by monitoring the C-2 protons of the four histidine residues. The intermediate contains one residue (X) in a partly folded environment and the other three residues in unfolded environments. The composite resonance (U) of these three protons at 10 °C agrees with the average chemical shift of the histidine residues in heat-unfolded ribonuclease A at high temperatures. During refolding at 10 °C, the resonance intensities of U and X disappear at the same rate that the spectrum of native ribonuclease A is regained.Partial deuteration experiments show that X is either histidine 12 or 119. Comparative studies of the amino-terminal fragment 1–20 of ribonuclease A indicate that X is histidine 12. The appearance of structure in this peptide can be followed by temperature-dependent changes in the chemical shift of histidine 12. At 10 °C the chemical shifts of histidine 12 and X agree closely. These results are consistent with the circular dichroism study of peptide 1–13 by Brown &; Klec (1971), who concluded that helix formation occurs at low temperatures.     

On the analysis of futile cycles in metabolism

So-called futile cycles in cellular metabolism consist of paired opposing reactions that, if simultaneously operant, act only to degrade free energy of ATP to heat. Previous considerations of the behavior of such substrate cycles have indicated their possible usefulness in regulating flux along metabolic pathways, but such analyses have treated the cycles in isolation, i.e. without taking into account the effects of enzymatic inputs to and outputs from the cycle. We here develop models of three typical substrate cycles that include enzymatic inputs to and outputs from the cycle and allow the enzymes of the cycles per se to be subject to a variety of allosteric modulations. The non-linear equations which describe these models were solved by an iterative procedure for sets of parameter values of metabolic interest. The results, when analyzed using appropriate definitions of regulatory sensitivity and energetic futility, demonstrate that the effects of the enzymes leading into and out of the cycle may cause profound changes in the operation of the substrate cycle and therefore may not be ignored. We find that the structural differences among the three cycles considered here result in corresponding functional differences. Our results suggest that (1) the fructose-6-P/fructose-1,6-di-P cycle acts effectively to gate bidirectional flux, but doesn't appreciably enhance regulation of unidirectional flux, (2) the glucose/glucose-6-P cycle is well suited to perform a homeostatic function and to adjust the set points for these two metabolites, and (3) the cycle at the pyruvate crossroads functions largely as a complex switch box that directs metabolic flow towards gluconeogenesis or glycolysis not only in response to inputs of or requirements for oxaloacetate, pyruvate, and phosphoenolpyruvate, but also in response to the combined action of allosteric modulators on the individual enzymes of this substrate cycle.     

Purification and characterization of two isoenzymes of lipoxygenase from soybeans

A chromatographic procedure for the purification of two lipoxygenase isoenzymes (linoleate: O₂ oxidoreductase, EC 1.13.11.12.) from soybean is described. The procedure for the purification of isoenzyme L-1 includes optimalized extraction, ammonium sulfate fractionation, heat treatment and gradient elution from a CM-Sephadex C-50 column. The purification of L-2 includes ammonium sulfate fractionation, gelfiltration on Sephadex G-150 and gradient elution from a DEAE-cellulose column. Both isoenzymes L-1 and L-2 appear homogeneous after Disc-PAGE. The isoelectric points are 5.6 for L-1 and 5.8 for L-2. Molecular weights are estimated as 100,000 for L-1 as well as L-2 applying three different methods. Both isoenzymes contain 0.9 mol iron per mol protien. The estimated turn over numbers are 8,200 mol linoleate per mol enzyme and min for L-1 and 3,100 for L-2. Amino acid compositions determined after acid hydrolysis show marked differences between L-1 and L-2, particularly with respect to the amino acids Lys, Phe, Ser, Gly and Leu. L-1 posesses a total of 9 cysteine molecules, 6 of which are present as disulfide bonds. L-2 posesses a total of 8 cysteine molecules with only one disulfide bond.These results have been presented in part at the 13th ISF Congress in Marseille on 2nd September 1976     

Substance P but not vasoactive intestinal peptide modulates immunoglobulin secretion in murine schistosomiasis.

Neuropeptides including SP and VIP modulate Ig secretion by in vitro stimulated lymphocyte cultures. It is not known whether these neuropeptides effect the B cell directly, or if they significantly alter humoral immune responses to pathogens. We have previously shown that granulomas derived from schistosome-infected mice contain immunoglobulin secreting B cells (ISC) as well as eosinophils that secrete substance P (SP) and vasoactive intestinal peptide (VIP). It therefore seemed plausible that B cells derived from infected animals might respond to these neuropeptides, and that such responses might effect immunoregulatory signals. In this study, we addressed these issues in the murine Schistosoma mansoni model, at the level of immunoglobulin secretion in single B cells. Spontaneous ISC were observed in both splenic and granuloma cell preparations. The addition of SP resulted in a dose-dependent reduction in the number and size of plaques (a 50% reduction was observed at 10(-9) M). This effect was blocked with SP antagonists. Similar results were observed in T cell-depleted cell cultures. VIP had no effect on ISC number or plaque size. We conclude that SP, but not VIP, decreases spontaneous ISC number and Ig secretion in short-term cultures of spleen and granuloma cells. SP appears to exert its effects at the level of single B cells through a receptor-mediated mechanism and may thus play an immunoregulatory role in schistosomiasis.     

Monoclonal antibodies raised against post-translational domains of the electroplax sodium channel

Summary Eleven monoclonal antibodies were identified that recognized eel electroplax sodium channels. All the monoclonal antibodies specifically immunostained the mature TTX-sensitive sodium channel (M _r 265,000) on immunoblots. None of the monoclonal antibodies would precipitate the in vitro translated channel core polypeptide in solution. One monoclonal antibody, 3G4, was found to bind to an epitope involving terminal polysialic acids. Extensive digestion of the channel by the exosialidase, neuraminidase, or partial polysialic acid removal bythe endosialidase, endo-N-acetylneuraminidase, destroy the 3G4 epitope, 3G4 is, therefore, a highly selective probe for the post-translationally attached polysialic acids. Except for this monoclonal antibody, the epitopes recognized by the remaining antibodies were highly resistant to extensive N-linked deglycosylation. Thus, the monoclonal antibodies may be directed against unique post-translationally produced domains of the electroplax sodium channel, presumably sugar groups that are abundant on this protein (Miller, J.A., Agnew, W.S., Levinson, S.R. 1983.Biochemistry 22:462–470). These monoclonal antibodies should prove useful as tools to study discrete post-translational processing events in sodium channel biosynthesis.