Theoretical treatment of hydrogen-ion effects on hydrolytic enzyme systems involving two enzyme-substrate complexes

1967 ◽  
Vol 71 (12) ◽  
pp. 3888-3901 ◽  
Author(s):  
James Allen Stewart ◽  
Hung Suen Lee
Keyword(s):  
Hydrolytic Enzyme ◽  
Hydrogen Ion ◽  
Theoretical Treatment ◽  
Enzyme Substrate ◽  
Enzyme Systems ◽  
Ion Effects

scholarly journals The effects of hydrogen ion concentration on the simplest steady-state enzyme systems

1971 ◽  
Vol 123 (3) ◽  
pp. 445-453 ◽  
Author(s):  
P. Ottolenghi
Keyword(s):  
Steady State ◽  
Active Site ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Hydrogen Ion Concentration ◽  
Substrate Complex ◽  
Perturbation Term ◽  
Enzyme Substrate ◽  
Enzyme Systems ◽  
Steady State Kinetics

Laidler (1955) showed that consideration of the effect of pH on enzymic mechanisms that obey steady-state kinetics leads to the inclusion in the equations of a ‘perturbation term’ that can introduce curvature into the Lineweaver–Burk plots. He also stated conditions in which this term vanishes. This term can lead to apparent activation by substrate. Further, several cases are shown in which simplification, but not disappearance, of the perturbation term can lead to linearity of Lineweaver–Burk plots. These cases arise when the ionization of groups at the active site either is unaffected or is completely prevented when the enzyme–substrate complex is formed. It is also shown that V(app.) can vary with pH without a concomitant change in Km(app.) in certain cases that obey steady-state kinetics without implying that Km=Ks. When the perturbation term is significant, Dixon's (1953) rules for the calculation of pK values will not always apply.

THEORY OF THE TRANSIENT PHASE IN KINETICS, WITH SPECIAL REFERENCE TO ENZYME SYSTEMS: II. THE CASE OF TWO ENZYME–SUBSTRATE COMPLEXES

1956 ◽  
Vol 34 (2) ◽  
pp. 146-150 ◽  
Author(s):  
Ludovic Ouellet ◽  
Keith J. Laidler
Keyword(s):  
Steady State ◽  
Substrate Concentration ◽  
Kinetic Scheme ◽  
Rate Equations ◽  
Theoretical Treatment ◽  
Transient Phase ◽  
Enzyme Substrate ◽  
Enzyme Systems ◽  
Steady State Rate ◽  
State Rate

A theoretical treatment is worked out for the kinetic scheme[Formula: see text]in which two enzyme–substrate complexes are formed consecutively. The steady-state rate equations are obtained, and equations are given for the transient phase subject to the condition that the substrate concentration is greatly in excess of that of the enzyme. Some kinetic consequences of the resulting equations are discussed.

THEORY OF THE TRANSIENT PHASE IN AN ENZYME SYSTEM INVOLVING TWO ENZYME-SUBSTRATE COMPLEXES: THE CASE OF THE FORMATION OF PRODUCTS FROM THE FIRST COMPLEX

1959 ◽  
Vol 37 (4) ◽  
pp. 737-743 ◽  
Author(s):  
Ludovic Ouellet ◽  
James A. Stewart
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Active Site ◽  
Substrate Concentration ◽  
Enzyme System ◽  
Kinetic Scheme ◽  
Enzyme Concentration ◽  
Theoretical Treatment ◽  
Transient Phase ◽  
Enzyme Substrate

A theoretical treatment is worked out for the kinetic scheme[Formula: see text]in which the concentration of P1 is followed. The steady-state and transient phase equations are obtained subject to the condition that the substrate concentration is greatly in excess of the enzyme concentration. The conditions under which evidence in favor of this mechanism can be obtained from experimental data are discussed. Under certain conditions, the weight of the enzyme corresponding to one active site can be determined. Methods for the evaluation of the different constants are described.

Hydrogen ion effects of the vertebrate photoreceptor

1978 ◽  
Vol 188 (1) ◽  
pp. 105-113 ◽  
Author(s):  
Clark Gedney ◽  
Sanford E. Ostroy
Keyword(s):  
Hydrogen Ion ◽  
Vertebrate Photoreceptor ◽  
Ion Effects

Metabolic and respiratory hydrogen ion effects on hypoxic pulmonary vasoconstriction

1984 ◽  
Vol 57 (2) ◽  
pp. 545-550 ◽  
Author(s):  
C. Marshall ◽  
L. Lindgren ◽  
B. E. Marshall
Keyword(s):  
Pressor Response ◽  
Hypoxic Pulmonary Vasoconstriction ◽  
Respiratory Acidosis ◽  
Hydrogen Ion ◽  
Regression Equations ◽  
Rat Lung ◽  
Pulmonary Vasoconstriction ◽  
Pressor Responses ◽  
Ion Effects

Hypoxic pulmonary vasoconstriction (HPV) was studied in the ventilated-perfused rat lung in vitro. Respiratory acidosis and alkalosis were obtained by ventilating with 2, 7, or 10% CO2 (21% O2-balance N2). Metabolic acidosis and alkalosis were produced by the addition of 0.9 N NaHCO3 or 1 N lactic acid to the perfusate at constant PCO2. At each pH the pressor responses to 2 and 4% O2 were compared with the maximum pressor response (R%max) obtained with zero O2 and 5% CO2 at a normal pH (approximately 7.35). HPV was maximal when the [H+] was between 38 and 50 nM and was attenuated by changes of pH in either direction. Both respiratory and metabolic pH changes had similar effects. The combined linear regression equations were as follows: with 2% O2 the response to acidosis was R%max = 101.37 – 0.52 [H+] and to alkalosis was R%max = 2.03 [H+] - 3.85; with 4% O2 the response to acidosis was R%max = 56.88 – 0.3 [H+] and to alkalosis was R%max = 1.16 [H+] - 4.95. These effects were not due to changes of ionized calcium.

Divalent cation and hydrogen ion effects on the structure and surface activity of pulmonary surfactant

Biochemistry ◽  
1987 ◽  
Vol 26 (24) ◽  
pp. 7986-7993 ◽  
Author(s):  
Hava Efrati ◽  
Samuel Hawgood ◽  
Mary C. Williams ◽  
Keelung Hong ◽  
Bradley J. Benson
Keyword(s):  
Surface Activity ◽  
Divalent Cation ◽  
Pulmonary Surfactant ◽  
Hydrogen Ion ◽  
Ion Effects

THE ENOLASE OF THE HUMAN ERYTHROCYTE

1962 ◽  
Vol 40 (1) ◽  
pp. 1005-1018
Author(s):  
Rhoda Blostein ◽  
Orville F. Denstedt
Keyword(s):  
Kinetic Study ◽  
Human Erythrocyte ◽  
Hydrogen Ion ◽  
Active Complex ◽  
Ion Concentrations ◽  
Enzyme Substrate ◽  
Low Concentrations ◽  
Absolute Requirement ◽  
Wide Range ◽  
High Concentrations

The enolase activity of the human erythrocyte has been studied with a partially purified preparation of the enzyme. The enzyme was found to have an absolute requirement for Mg2+ions. A kinetic study of the influence of the concentration of Mg ions and 2-phosphoglycerate on the formation of phosphoeno/pyruvate from 2-phosphoglycerate has shown that the active complex of enzyme, substrate, and activator (Mg2+) can be formed in several ways. With low concentrations of substrate and Mg2+the reaction was maximum at pH 7.0; with high concentrations of both, the activity was maximum over a wide range of hydrogen ion concentrations on the acid side of neutrality (at least from pH 6.3 to 7.0) and decreased above pH 7.0.

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