The anticalmodulin effect of aflatoxin B1 on purified erythrocyte Ca2+-AtPase

1995 ◽  
Vol 15 (4) ◽  
pp. 209-220 ◽  
Author(s):  
Aderonke O. Adebayo ◽  
Gbolahan W. Okunade ◽  
Olufunso O. Olorunsogo
Keyword(s):  
Atpase Activity ◽  
Aflatoxin B1 ◽  
Prolonged Exposure ◽  
Limited Proteolysis ◽  
Kinetic Studies ◽  
Phosphatidyl Serine ◽  
Binding Domain ◽  
Calmodulin Binding ◽  
Ionic Detergent ◽  
Solubilized Enzyme

The genotoxic carcinogen aflatoxin B1 (AFB1) inhibited the calmodulin-stimulated membrane-bound (Ca2+Mg2+)-ATPase. Using the purified enzyme, 12 nmoles per ml of AFB1 caused maximum inhibition of 28% and 50%, of the acidic phospholipid-stimulated and calmodulin-activated Ca2+-ATPase activity respectively. Treatment of red cell ghosts with increasing concentrations of Triton X-100, a non-ionic detergent caused a progressive loss of both the basal and calmodulin-stimulated Ca2+-ATPase activity. The activity of the phospholipid-free, detergent-solubilized enzyme was almost fully restored by phosphatidyl serine (PS) and its sensitivity to calmodulin was restored in the presence of phosphatidyl choline (PC). Analysis of the results obtained using varying concentrations of ATP shows that AFB1 did not affect the Km and Vmax of the unstimulated enzyme whereas these parameters were reduced by about 75% and 50%, respectively, in the presence of calmodulin. Using the product of limited proteolysis by trypsin i.e. the 90 kDa fragment which still retains its calmodulin binding-domain and the 76 kDa fragment which has lost this domain, kinetic studies on the enzyme activity revealed that AFB1 inhibited the calmodulin-activated 90 kDa fragment by about 50% while the 76 kDa was not affected at all by the toxin and calmodulin. The toxin had no significant affect on the basal activity of the 90 kDa limited proteolysis fragment of the enzyme. These observations suggest that AFB1 inhibits the activated Ca2+-ATPase by binding to an important site in the calmodulin-binding domain of the enzyme. It seems likely that the toxin binds to tryptophan in the calmodulin-binding domain, thus causing a reduction in the rate at which this domain can interact with Ca2+-calmodulin or acidic phospholipids. The implication of these observations is that Ca2+-extrusion and other calmodulin-activated enzymes and processes may be slowed down during prolonged exposure to AFB1 because of its anticalmodulin effect.

scholarly journals Antibodies against erythrocyte Ca2+-transport ATPase specifically inhibit the calmodulin-dependent fraction of the enzyme's activity

1985 ◽  
Vol 228 (2) ◽  
pp. 479-485 ◽  
Author(s):  
K Gietzen ◽  
J Kolandt
Keyword(s):  
Smooth Muscle ◽  
Plasma Membrane ◽  
Oleic Acid ◽  
Atpase Activity ◽  
Binding Site ◽  
Rat Brain ◽  
Limited Proteolysis ◽  
Transport Atpase ◽  
Calmodulin Binding ◽  
Muscle Plasma Membrane

Antibodies against purified Ca2+-transport ATPase from human erythrocytes were raised in rabbits. Immunodiffusion experiments revealed that precipitating antibodies had been developed. The immunoglobulin fraction inhibited solely the calmodulin-dependent fraction of erythrocyte Ca2+-transport ATPase activity, whereas the basal (in the absence of added calmodulin) activity of the enzyme was not significantly affected by the antibodies. The antibodies produced similar doseresponse curves for the calmodulin- and the oleic acid-stimulated enzyme. However, the immunoglobulin fraction was considerably less effective in inhibiting Ca2+-transport ATPase activated by limited proteolysis. The results obtained with our antibodies are compatible with the interpretation that at least one subpopulation of the antibodies attacks the enzyme at or close to the calmodulin-binding site of the ATPase. The antibodies also inhibited the calmodulin-regulated Ca2+-transport ATPase from pig smooth-muscle plasma membrane, though with lower potency. However, the immunoglobulin fraction failed to suppress pig cardiac sarcoplasmicreticulum Ca2+-transport ATPase activity in the concentration range investigated. In addition, the activity of phosphodiesterase from rat brain, another enzyme modulated by calmodulin, was not at all affected by the immunoglobulin fraction.

Limited Proteolysis of Vitronectin by Plasmin Destroys Heparin Binding Activity

1991 ◽  
Vol 66 (03) ◽  
pp. 310-314 ◽  
Author(s):  
David C Sane ◽  
Tammy L Moser ◽  
Charles S Greenberg
Keyword(s):  
Limited Proteolysis ◽  
Plasminogen Activator Inhibitor ◽  
Binding Activity ◽  
Binding Domain ◽  
Heparin Binding ◽  
Inhibitor Type ◽  
Activator Inhibitor Type ◽  
Activator Inhibitor ◽  
Pai 1

SummaryVitronectin (VN) stabilizes plasminogen activator inhibitor type 1 (PAI-1) activity and prevents the fibrin(ogen)-induced acceleration of plasminogen activation by t-PA. These antifibrinolytic activities as well as other functions are mediated by the glycosaminoglycan (GAG) binding domain of VN. Since the GAG binding region is rich in arginyl and lysyl residues, it is a potential target for enzymes such as plasmin. In this paper, the dose and time-dependent proteolysis of VN by plasmin is demonstrated. The addition of urokinase or streptokinase (200 units/ml) to plasma also produced proteolysis of VN. With minimal proteolysis, the 75 kDa band was degraded to a 62-65 kDa form of VN. This minimal proteolysis destroyed the binding of [3H]-heparin to VN and reversed the neutralization of heparin by VN.Thus, the plasmin-mediated proteolysis of the GAG binding activity of VN could destroy the antifibrinolytic activity of VN during physiologic conditions and during thrombolytic therapy. Furthermore, other functions of VN in complement and coagulation systems that are mediated by the GAG binding domain may be destroyed by plasmin proteolysis.

scholarly journals Modulation of erythrocyte Ca2+-ATPase by selective calpain cleavage of the calmodulin-binding domain

1989 ◽  
Vol 264 (14) ◽  
pp. 8289-8296 ◽  
Author(s):  
P James ◽  
T Vorherr ◽  
J Krebs ◽  
A Morelli ◽  
G Castello ◽  
...  
Keyword(s):  
Binding Domain ◽  
Calmodulin Binding

scholarly journals The Calmodulin Binding Domain of the Plasma Membrane Ca2+ Pump Interacts Both with Calmodulin and with Another Part of the Pump

1989 ◽  
Vol 264 (21) ◽  
pp. 12313-12321 ◽  
Author(s):  
A Enyedi ◽  
T Vorherr ◽  
P James ◽  
D J McCormick ◽  
A G Filoteo ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Binding Domain ◽  
Calmodulin Binding

Phosphate Binding to Isolated Chloroplast Coupling Factor (CF1)

1988 ◽  
Vol 43 (3-4) ◽  
pp. 213-218 ◽  
Author(s):  
Bernhard Huchzermeyer
Keyword(s):  
Atpase Activity ◽  
Binding Site ◽  
Inorganic Phosphate ◽  
Coupling Factor ◽  
Binding Domain ◽  
Atp Binding ◽  
Phosphate Binding ◽  
Chloroplast Coupling Factor ◽  
Single Binding Site ◽  
Site Binding

A single binding site for phosphate was found on isolated chloroplast coupling factor in the absence of nucleotides. In our experiments the phosphate binding site showed a Kd of 170 μᴍ. We did not observe any differences whether the ATPase activity of CF] had been activated or not. If the enzyme was incubated with [γ-32P]ATP the amount of 32P bound per CF1 depended on the pretreatment of the enzyme: In the presence of ADP no ATP or phosphate was bound to CF,. After activation of ATPase activity one mol of ATP per mol CF, was rapidly bound and hydrolyzed while there was a slowly occurring binding of another phosphate without concomitant nucleotide binding. We conclude that there are two different types of phosphate binding observed in our experiments: 1) Inorganic phosphate can be bound by one catalytic site per mol of CF1 2) The γ-phosphate of ATP is able to bind to an ATP binding domain of the enzyme if this domain can exchange substrates with the incubation medium. This ATP binding domain appears to differ from the site binding inorganic phosphate, because at least a portion of the coupling factor contains more than one labelled phosphate during our ATPase tests.

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