scholarly journals Mg2+ is an essential activator of hydrolytic activity of membrane-bound pyrophosphatase of Rhodospirillum rubrum

1992 ◽  
Vol 283 (2) ◽  
pp. 561-566 ◽  
Author(s):  
A Sosa ◽  
H Ordaz ◽  
I Romero ◽  
H Celis
Keyword(s):  
Substrate Concentration ◽  
Rhodospirillum Rubrum ◽  
Hydrolytic Activity ◽  
Binding Kinetics ◽  
Catalytic Complex ◽  
Equilibrium Binding ◽  
Complex Membrane ◽  
Competitive Inhibitors ◽  
Membrane Bound

The substrate for the hydrolytic activity of membrane-bound pyrophosphatase is the PP(i)-Mg2+ complex. The enzyme has no activity when the free Mg2+ concentration is lower than 10 microM (at 0.5 mM-PP(i)-Mg2+), and therefore free Mg2+ is an essential activator of the hydrolytic activity. The Km for the substrate changes in response to variation in free Mg2+ concentration, from 10.25 to 0.6 mM when free Mg2+ is increased from 0.03 to 1.0 mM respectively. The Km for Mg2+ depends on the substrate concentration: the Km decreases from 0.52 to 0.14 mM from 0.25 to 0.75 mM-PP(i)-Mg2+ respectively. The extrapolated Km for Mg2+ in the absence of the substrate is 0.73 mM. Imidodiphosphate-Mg2+ and free Ca2+ were used as competitive inhibitors of substrate and activator respectively. The equilibrium binding kinetics suggest an ordered mechanism for the activator and the substrate: Mg2+ ions bind the enzyme before PP(i)-Mg2+ in the formation of the catalytic complex, membrane-bound pyrophosphatase-(Mg2+)-(PP(i)-Mg2+).

scholarly journals The determination of binding parameters when the total and free substrate concentrations are not approximately equal

1979 ◽  
Vol 179 (3) ◽  
pp. 697-700 ◽  
Author(s):  
N Gains
Keyword(s):  
Substrate Concentration ◽  
Graphical Method ◽  
Enzyme Concentration ◽  
Binding Parameters ◽  
Free Concentration ◽  
Equilibrium Binding ◽  
Substrate Concentrations

By using a standard graphical method values of Km and V may be found that are independent of the conditions and assumptions that the total substrate concentration approximates to its free concentration and that Km is much larger than the enzyme concentration. The procedure is also applicable to the determination of equilibrium binding parameters of a ligand to a macromolecule.

scholarly journals Binding Kinetics between Membrane-Bound Kinesin Motors and Microtubules

2019 ◽  
Vol 116 (3) ◽  
pp. 411a
Author(s):  
Rui Jiang ◽  
SooHyun Park ◽  
Steven Vandal ◽  
Erkan Tüzel ◽  
Sheereen Majd ◽  
...  
Keyword(s):  
Binding Kinetics ◽  
Membrane Bound

The β-glucosidases of porcine kidney

1977 ◽  
Vol 55 (2) ◽  
pp. 140-145 ◽  
Author(s):  
Julian N. Kanfer ◽  
Richard A. Mumford ◽  
Srinivasa S. Raghavan
Keyword(s):  
Sodium Taurocholate ◽  
Hydrolytic Activity ◽  
Acidic Ph ◽  
Porcine Kidney ◽  
Ph Optimum ◽  
Pig Kidney ◽  
Competitive Inhibitors ◽  
Triton X ◽  
Hydrolysis Of ◽  
Estradiol 17Β

Some of the properties of a partially purified particle bound and soluble β-glucosidase (EC 3.2.1.21) from pig kidney were compared. The soluble β-glucosidase (1) hydrolyzed 4-methylumbelliferyl-β-D-glucoside (4-MU-β-D-glucoside) 17α-estradiol 3β-glucoside, 17α-estradiol 17β-glucoside, and salicin, but not glucosylceramide, (2) possessed a broad pH optimum (5.5–7.0), (3) had an isoelectric point of 4.9, and (4) was inhibited by Triton X-100. Several compounds were found to be competitive inhibitors of its hydrolytic activity, gluconolactam and estrone β-glucoside being the most effective. In contrast, a particulate β-glucosidase purified from the same tissue (1) had an acidic pH optimum (5.0), (2) was stimulated by sodium taurocholate and 'Gaucher's factor' for the hydrolysis of both 4-MU-β-glucoside and glucosylceramide, and (3) was capable of catalyzing a transglucosylation reaction employing 4-MU-β-D-glucoside or glucosylceramide as the glucosyl donor, and [l4C]ceramide as acceptor.

Renal neutral α-d-glucosidase has no role in transport of d-glucose derived from maltose hydrolysis

1998 ◽  
Vol 274 (4) ◽  
pp. R1150-R1157
Author(s):  
Jean Giudicelli ◽  
Pascale Delque-Bayer ◽  
Pierre Sudaka ◽  
Jean-Claude Poiree
Keyword(s):  
Membrane Proteins ◽  
Membrane Vesicles ◽  
Hydrolytic Activity ◽  
The Other ◽  
Transmembrane Transport ◽  
Artificial Membrane ◽  
Enzyme Localization ◽  
Free Glucose ◽  
Membrane Bound ◽  
Rule Out

To reinvestigate the “hydrolase-related transport” concept, neutral α-d-glucosidase, a membrane-bound disaccharidase of renal proximal tubule, was first purified from brush-border membranes and then asymmetrically reincorporated into egg phosphatidylcholine vesicles. Proteolytic treatments and immunotitration studies demonstrated that this enzyme was integrated in native and artificial membrane vesicles with a similar topology. The uptake of free glucose and glucose produced by maltose hydrolysis was studied using 1) proteoliposomes containing integrated neutral α-d-glucosidase, in combination with other membrane proteins, and 2) proteoliposomes containing only the other membrane proteins but incubated in a medium containing neutral α-d-glucosidase in its hydrophilic form. No modification was observed in the uptake of freed-glucose or d-glucose produced by maltose hydrolysis, regardless of enzyme localization. In contrast to previous findings on the hydrolase-related transport concept, these results rule out any participation of neutral α-d-glucosidase in the transport of free glucose or glucose produced by maltose hydrolysis. Hydrolytic activity and transmembrane transport appear to be two independent and sequential steps.

PURIFICATION AND PROPERTIES OF AN INDUCIBLE β-GLUCOSIDASE OF BAKERS' YEAST

1966 ◽  
Vol 44 (8) ◽  
pp. 1099-1108 ◽  
Author(s):  
A. N. Inamdar ◽  
J. G. Kaplan
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Molecular Weight ◽  
Hydrolytic Activity ◽  
Chromogenic Substrate ◽  
Yeast Saccharomyces Cerevisiae ◽  
Intact Cells ◽  
Highly Active ◽  
Naturally Occurring ◽  
Purification And Properties ◽  
Competitive Inhibitors

The inducible β-glucosidase present in crude extracts of cellobiose-grown bakers' yeast (Saccharomyces cerevisiae C) was purified 50-fold and found to be homogeneous in the ultracentrifuge, with a molecular weight of 313,000. The enzyme was virtually identical in its properties with the internal, cryptic enzyme of the yeast cell, revealed by butanol treatment of the suspensions. It was unlike the membrane-localized enzyme found at the surface of intact cells in its low affinity for cellobiose and methyl-β-glucoside as substrates and inhibitors. The enzyme was specific for the β configuration and had no activity against substrates such as α-glucosides, β-galactosides, or β-xylosides. It was highly active against both naturally occurring and synthetic substrates with aromatic aglycones, and may thus be classed as an aryl-β-glucosidase. The enzyme had weak hydrolytic activity against methyl-β-glucoside and cellobiose, but these compounds, unlike all of the aryl-β-glucosides tested, were not competitive inhibitors of its activity against the chromogenic substrate pNPG. There were about 40,000 molecules of enzyme per cell in fully induced cultures and the enzyme represented about 3% of the total protein of these cells.

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