scholarly journals Structure of the glycosyl-phosphatidylinositol membrane anchor of acetylcholinesterase from the electric organ of the electric-fish, Torpedo californica

1993 ◽  
Vol 296 (2) ◽  
pp. 473-479 ◽  
Author(s):  
A Mehlert ◽  
L Varon ◽  
I Silman ◽  
S W Homans ◽  
M A J Ferguson
Keyword(s):  
Electric Fish ◽  
Electric Organ ◽  
Methylation Analysis ◽  
Membrane Anchor ◽  
Gpi Anchor ◽  
Torpedo Californica ◽  
Glycosyl Phosphatidylinositol ◽  
Anchor Structure

The structure of the glycan moiety of the glycosyl-phosphatidylinositol (GPI) membrane anchor from Torpedo californica (electric fish) electric-organ acetylcholinesterase was solved using n.m.r., methylation analysis and chemical and enzymic micro-sequencing. Two structures were found to be present: Glc alpha 1-2Man alpha 1-2Man alpha 1-6Man alpha 1-4GlcN alpha 1-6myo-inositol and Glc alpha 1-2Man alpha 1-2Man alpha 1-6(GalNAc beta 1-4)Man alpha 1-4GlcN alpha 1-6myo-inositol. The presence of glucose in this GPI anchor structure is a novel feature. The anchor was also shown to contain 2.3 residues of ethanolamine per molecule.

Phospholipase Resistance of the Glycosyl-Phosphatidylinositol Membrane Anchor on Human Alkaline Phosphatase

1992 ◽  
Vol 38 (12) ◽  
pp. 2517-2525 ◽  
Author(s):  
Y W Wong ◽  
M G Low
Keyword(s):  
Alkaline Phosphatase ◽  
Cell Surface ◽  
Human Cell Lines ◽  
Membrane Anchor ◽  
Gpi Anchor ◽  
Glycosyl Phosphatidylinositol ◽  
In Vivo Release ◽  
Mammalian Tissues ◽  
Inositol Ring

Abstract Alkaline phosphatase (ALP) is attached to the cell surface in mammalian tissues via a glycosyl-phosphatidylinositol (GPI) anchor and can be released from the membrane by GPI-specific phospholipases. In a range of cultured human cell lines, however, the sensitivity of ALP to phospholipases was observed to be variable in magnitude (approximately 20-90%). The mechanism of phospholipase resistance was explored with phospholipases of different bond specificities. The results suggest that phospholipase resistance is the result of acylation of the inositol ring in the GPI anchor. The occurrence of phospholipase-resistant forms of ALP may have important implications for the in vivo release and disposition of plasma ALP.

scholarly journals Soluble low-Km 5′-nucleotidase from electric-ray (Torpedo marmorata) electric organ and bovine cerebral cortex is derived from the glycosyl-phosphatidylinositol-anchored ectoenzyme by phospholipase C cleavage

1992 ◽  
Vol 284 (3) ◽  
pp. 621-624 ◽  
Author(s):  
M Vogel ◽  
H Kowalewski ◽  
H Zimmermann ◽  
N M Hooper ◽  
A J Turner
Keyword(s):  
Cerebral Cortex ◽  
Phospholipase C ◽  
High Speed ◽  
Electric Organ ◽  
Bovine Brain ◽  
Soluble Enzyme ◽  
Torpedo Marmorata ◽  
Gpi Anchor ◽  
Glycosyl Phosphatidylinositol ◽  
Membrane Bound

Soluble and membrane-bound low-Km 5′-nucleotidase was isolated from high-speed supernatants and membrane fractions derived from the electric organ of the electric ray (Torpedo marmorata) or from bovine brain cerebral cortex. Purification of both enzymes included chromatography on concanavalin A-Sepharose and AMP-Sepharose. The contribution to the total of soluble enzyme activity was lower in electric organ (1.6%) than in bovine cerebral cortex (27.9%). Membrane-bound and soluble forms have very similar Km values for AMP and are inhibited by micromolar concentrations of ATP. Both forms cross-react with, and are inhibited by, an antibody against the membrane-bound surface-located (ecto-) 5′-nucleotidase from electric organ. The HNK-1 carbohydrate epitope is present on both forms of the Torpedo enzyme, but is entirely absent from bovine cerebral-cortex 5′-nucleotidase. An antibody specific for the inositol 1,2-(cyclic)monophosphate that is formed on phospholipase C cleavage of an intact glycosyl-phosphatidylinositol (GPI) anchor binds to the soluble, but not to the membrane-bound, form of the enzyme from both sources. Our results suggest that soluble low-Km 5′-nucleotidase in both electric organ and bovine brain is derived from the membrane-bound GPI-anchored form of the enzyme by the action of a phospholipase C and is not a soluble cytoplasmic enzyme.

scholarly journals The weakly electric fish, Apteronotus albifrons, actively avoids experimentally induced hypoxia

2021 ◽  
Author(s):  
Stefan Mucha ◽  
Lauren J. Chapman ◽  
Rüdiger Krahe
Keyword(s):  
Active Avoidance ◽  
Electric Fish ◽  
Electric Organ ◽  
The Other ◽  
Weakly Electric Fish ◽  
Dissolved Oxygen Concentration ◽  
Shuttle Box ◽  
Freshwater Habitats ◽  
Electric Organ Discharges ◽  
Weakly Electric

AbstractAnthropogenic environmental degradation has led to an increase in the frequency and prevalence of aquatic hypoxia (low dissolved oxygen concentration, DO), which may affect habitat quality for water-breathing fishes. The weakly electric black ghost knifefish, Apteronotus albifrons, is typically found in well-oxygenated freshwater habitats in South America. Using a shuttle-box design, we exposed juvenile A. albifrons to a stepwise decline in DO from normoxia (> 95% air saturation) to extreme hypoxia (10% air saturation) in one compartment and chronic normoxia in the other. On average, A. albifrons actively avoided the hypoxic compartment below 22% air saturation. Hypoxia avoidance was correlated with upregulated swimming activity. Following avoidance, fish regularly ventured back briefly into deep hypoxia. Hypoxia did not affect the frequency of their electric organ discharges. Our results show that A. albifrons is able to sense hypoxia at non-lethal levels and uses active avoidance to mitigate its adverse effects.

scholarly journals A sodium-activated potassium channel supports high-frequency firing and reduces energetic costs during rapid modulations of action potential amplitude

2013 ◽  
Vol 109 (7) ◽  
pp. 1713-1723 ◽  
Author(s):  
Michael R. Markham ◽  
Leonard K. Kaczmarek ◽  
Harold H. Zakon
Keyword(s):  
Action Potential ◽  
High Frequency ◽  
Electric Fish ◽  
Electric Organ Discharge ◽  
Electric Organ ◽  
Weakly Electric Fish ◽  
Energetic Costs ◽  
Dynamic Regulation ◽  
Voltage Gated

We investigated the ionic mechanisms that allow dynamic regulation of action potential (AP) amplitude as a means of regulating energetic costs of AP signaling. Weakly electric fish generate an electric organ discharge (EOD) by summing the APs of their electric organ cells (electrocytes). Some electric fish increase AP amplitude during active periods or social interactions and decrease AP amplitude when inactive, regulated by melanocortin peptide hormones. This modulates signal amplitude and conserves energy. The gymnotiform Eigenmannia virescens generates EODs at frequencies that can exceed 500 Hz, which is energetically challenging. We examined how E. virescens meets that challenge. E. virescens electrocytes exhibit a voltage-gated Na+current ( INa) with extremely rapid recovery from inactivation (τrecov= 0.3 ms) allowing complete recovery of Na+current between APs even in fish with the highest EOD frequencies. Electrocytes also possess an inwardly rectifying K+current and a Na+-activated K+current ( IKNa), the latter not yet identified in any gymnotiform species. In vitro application of melanocortins increases electrocyte AP amplitude and the magnitudes of all three currents, but increased IKNais a function of enhanced Na+influx. Numerical simulations suggest that changing INamagnitude produces corresponding changes in AP amplitude and that KNachannels increase AP energy efficiency (10–30% less Na+influx/AP) over model cells with only voltage-gated K+channels. These findings suggest the possibility that E. virescens reduces the energetic demands of high-frequency APs through rapidly recovering Na+channels and the novel use of KNachannels to maximize AP amplitude at a given Na+conductance.

scholarly journals Structure of the glycosyl-phosphatidylinositol membrane anchor of the Leishmania major promastigote surface protease.

1990 ◽  
Vol 265 (28) ◽  
pp. 16955-16964 ◽  
Author(s):  
P Schneider ◽  
M A Ferguson ◽  
M J McConville ◽  
A Mehlert ◽  
S W Homans ◽  
...  
Keyword(s):  
Leishmania Major ◽  
Membrane Anchor ◽  
Glycosyl Phosphatidylinositol

Sensory coding and corollary discharge effects in mormyrid electric fish

1989 ◽  
Vol 146 (1) ◽  
pp. 229-253 ◽  
Author(s):  
C. C. Bell
Keyword(s):  
Electric Fish ◽  
Spatial Information ◽  
Electric Organ Discharge ◽  
Low Frequency ◽  
Electric Organ ◽  
Motor Command ◽  
Corollary Discharge ◽  
Weakly Electric Fish ◽  
Central Projection ◽  
Sensory Coding

Weakly electric fish use their electrosensory systems for electrocommunication, active electrolocation and low-frequency passive electrolocation. In electric fish of the family Mormyridae, these three purposes are mediated by separate classes of electroreceptors: electrocommunication by Knollenorgan electroreceptors, active electrolocation by Mormyromast electroreceptors and low-frequency passive electrolocation by ampullary electroreceptors. The primary afferent fibres from each class of electroreceptors terminate in a separate central region. Thus, the mormyrid electrosensory system has three anatomically and functionally distinct subsystems. This review describes the sensory coding and initial processing in each of the three subsystems, with an emphasis on the Knollenorgan and Mormyromast subsystems. The Knollenorgan subsystem is specialized for the measurement of temporal information but appears to ignore both intensity and spatial information. In contrast, the Mormyromast subsystem is specialized for the measurement of both intensity and spatial information. The morphological and physiological characteristics of the primary afferents and their central projection regions are quite different for the two subsystems and reflect the type of information which the subsystems preserve. This review also describes the electric organ corollary discharge (EOCD) effects which are present in the central projection regions of each of the three electrosensory subsystems. These EOCD effects are driven by the motor command that drives the electric organ to discharge. The EOCD effects are different in each of the three subsystems and these differences reflect differences in both the pattern and significance of the sensory information that is evoked by the fish's own electric organ discharge. Some of the EOCD effects are invariant, whereas others are plastic and depend on previous afferent input. The mormyrid work is placed within two general contexts: (a) the measurement of time and intensity in sensory systems, and (b) the various roles of motor command (efferent) signals and self-induced sensory (reafferent) signals in sensorimotor systems.

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