TonB protein and energy transduction between membranes

TonB protein couples cytoplasmic membrane electrochemical potential to active transport of iron-siderophore complexes and vitamin B12 through high-affinity outer membrane receptors of Gram-negative bacteria. The mechanism of energy transduction remains to be determined, but important concepts have already begun to emerge. Consistent with its function, TonB is anchored in the cytoplasmic membrane by its uncleaved amino terminus while largely occupying the periplasm. Both the connection to the cytoplasmic membrane and the amino acid sequences of the anchor are essential for activity. TonB directly associates with a number of envelope proteins, among them the outer membrane receptors and cytoplasmic membrane protein ExbB. ExbB and TonB interact through their respective transmembrane domains. ExbB is proposed to recycle TonB to an active conformation following energy transduction to the outer membrane. TonB most likely associates with the outer membrane receptors through its carboxy terminus, which is required for function. In contrast, the novel prolinerich region of TonB can be deleted without affecting function. A model that incorporates this information, as well as tempered speculation, is presented.     

Time course of color induction in the honeybee

Color induction in the honeybee is investigated in color discrimination experiments. An individual bee walks in a dark arena and is trained to a self-luminant stimulus presented from below. In the dual-choice tests the dark background is replaced by a colored induction stimulus. Choice behavior is recorded by TV camera and analyzed by computer. Successive color induction is separated from simultaneous induction by analysis of the walking paths. Only successive color induction occurs. Simultaneous effects are not observed. That is a stimulus acts as a color inducing stimulus only when the bee crosses this stimulus. Thus, the color perceived by a given eye region is found to be dependent on the viewing history, but not on the stimuli presented simultaneously on neighboring parts of the retina. Color induction in the honeybee described in terms of selective sensitivity decrease (adaptation) does not explain all behavioral effects induced by the stimulus. The time course of successive color induction is calculated from the exposure times to the induction stimulus and from the choice behavior. The data suggest that color induction is complete after a few seconds. Photoreceptor adaptation is sufficient to explain the observed time course.     

Biochemical composition of the parasitic amphipod Hyperia galba in relation to age and starvation

Summary Hyperia galba was collected in the waters around Helgoland and in the Weser-Elbe-estuary during autumn. Its mode of life is a temporary but obligatory parasitism. The basal biochemical composition of the adults was analyzed in detail and related to the fresh, dry, and ash-free dry weight as well as sex and body length. Hyperia galba (males/females) consists of 85/86% water; the dry matter contains approximately 64/61% protein, 10/11% lipid, 1.2/1.5% carbohydrate, 10/8% chitin, and 23/23% ash. The analyses of basal elemental composition yielded approximately 38% C, 9% N and 6% H. Under natural conditions, individuals may encounter at least two periods of food shortage during their lives. Therefore, the analyses were carried out on individuals of different developmental stages also under food deprivation. The data are discussed with respect to the special mode of life of the species and compared with those found by other authors in several related crustacean species.Abbreviations AFDW ash-free dry weight - BL body length - DW dry weight - SD standard deviation - WW wet weight     

Regeneration from crayfish phasic and tonic motor axons in vitro

An explant culture system is described that allows examination of axonal growth from the tonically and phasically active motoneurons of the abdominal nerve cord of the crayfish. In this preparation, growth occurs from the cut end of the axon while the remainder of the motoneuron is undisturbed. In vitro growth from the branches of the third roots, which contain the axons from the tonic and phasic motoneurons of abdominal ganglia one through four, was verified as axonal by retrograde labeling of axons and neuronal somata within the nerve cord. Growth from the axons of phasic and tonic cells was observed as early as 24 h after plating and continued for an additional 7–10 days. The morphology and growth rates of the motor terminals differed between the tonic and phasic axons. The phasic axons grew significantly faster and branched more often than did the tonic motor axons. These differences in growth may be related to differences in motoneuron size or, may result from differences in electrical activity. Tonic motoneurons show spontaneous impulse activity for up to 6 days in culture, whereas phasic motoneurons show no spontaneous impulse activity. In addition, the differences in growth may be related to the morphological differences in tonic and phasic motor terminals observed in situ. © 1993 John Wiley & Sons, Inc.     

Profiling SARS-CoV-2 HLA-I peptidome reveals T cell epitopes from out-of-frame ORFs

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