Heterogeneous catalysis by phospholipase A2: formulation of a kinetic description of surface effects

1979 ◽  
Vol 57 (1) ◽  
pp. 97-106 ◽  
Author(s):  
David O. Tinker ◽  
Jane Wei
Keyword(s):  
Fatty Acid ◽  
Crystalline Phase ◽  
Liquid Crystalline ◽  
Surface Effects ◽  
Liquid Crystalline Phase ◽  
Desorption Rate ◽  
Substrate Complex ◽  
Steady State Kinetics ◽  
Mechanism Of Catalysis ◽  
Hydrolysis Of

The kinetics of hydrolysis of aqueous dispersions of long-chain, saturated phosphatidylcholines (PC) catalysed by Crotalus atrox phospholipase A2 (PLA) have been analysed, and a reaction mechanism proposed which takes surface effects into account. PLA is proposed to form an enzyme–substrate complex with surface substrate molecules, thereby undergoing a conformational change which exposes sites that interact with the lipid surface. After a hydrolytic event, the enzyme can either desorb from the surface (path 1), or diffuse along the surface to an adjacent substrate molecule (path 2). The path 1 dominated mechanism leads to Michaelis–Menten steady-state kinetics, and characterizes hydrolysis of gel phase PC. Evidence for saturation of the surface with PLA was obtained at high enzyme concentrations. The path 2 mechanism dominates when the desorption rate is very small; this mechanism describes hydrolysis of liquid crystalline phase PC and is characterized by an initial burst of hydrolysis followed by a very slow reaction. The velocities in these two phases of the reaction are independent of bulk PC concentration. When gel and liquid crystalline PC phases coexist, as in mixtures of dimyristoyl- and distearoyl-PC, the liquid crystalline phase is preferentially hydrolysed. Products of the reaction (lyso-PC and fatty acid) stimulate hydrolysis, apparently by stimulating desorption of PLA. The desorption rate constant appears to be a linear function of the surface concentrations of lyso-PC and fatty acid. The proposed model describes hydrolysis progress curves extremely well and is consistent with current ideas on the mechanism of catalysis by this enzyme.

scholarly journals Electron transfer studies of a conventional redox probe in human sweat and saliva bio-mimicking conditions

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
P. Krishnaveni ◽  
V. Ganesh
Keyword(s):  
Electron Transfer ◽  
Crystalline Phase ◽  
Liquid Crystalline ◽  
Transfer Reaction ◽  
Electron Transfer Reaction ◽  
Redox Couple ◽  
Liquid Crystalline Phase ◽  
Transfer Reactions ◽  
Redox Probe ◽  
Human Sweat

AbstractModern day hospital treatments aim at developing electrochemical biosensors for early diagnosis of diseases using unconventional human bio-fluids like sweat and saliva by monitoring the electron transfer reactions of target analytes. Such kinds of health care diagnostics primarily avoid the usage of human blood and urine samples. In this context, here we have investigated the electron transfer reaction of a well-known and commonly used redox probe namely, potassium ferro/ferri cyanide by employing artificially simulated bio-mimics of human sweat and saliva as unconventional electrolytes. Typically, electron transfer characteristics of the redox couple, [Fe(CN)6]3−/4− are investigated using electrochemical techniques like cyclic voltammetry and electrochemical impedance spectroscopy. Many different kinetic parameters are determined and compared with the conventional system. In addition, such electron transfer reactions have also been studied using a lyotropic liquid crystalline phase comprising of Triton X-100 and water in which the aqueous phase is replaced with either human sweat or saliva bio-mimics. From these studies, we find out the electron transfer reaction of [Fe(CN)6]3−/4− redox couple is completely diffusion controlled on both Au and Pt disc shaped electrodes in presence of sweat and saliva bio-mimic solutions. Moreover, the reaction is partially blocked by the presence of lyotropic liquid crystalline phase consisting of sweat and saliva bio-mimics indicating the predominant charge transfer controlled process for the redox probe. However, the rate constant values associated with the electron transfer reaction are drastically reduced in presence of liquid crystalline phase. These studies are essentially carried out to assess the effect of sweat and saliva on the electrochemistry of Fe2+/3+ redox couple.

Liquid crystalline phase transitions in hexakis(4-(4′-heptyloxy)biphenoxy)cyclotriphosphazene

1995 ◽  
Vol 18 (5) ◽  
pp. 795-800 ◽  
Author(s):  
K. Moriya ◽  
H. Mizusaki ◽  
M. Kato ◽  
S. Yano ◽  
M. Kajiwara
Keyword(s):  
Phase Transitions ◽  
Crystalline Phase ◽  
Liquid Crystalline ◽  
Liquid Crystalline Phase

scholarly journals Influence of applied electric fields on the positive magneto-LC effects observed in the ferroelectric liquid crystalline phase of a chiral nitroxide radical compound

Soft Matter ◽  
2013 ◽  
Vol 9 (18) ◽  
pp. 4687 ◽  
Author(s):  
Katsuaki Suzuki ◽  
Yoshiaki Uchida ◽  
Rui Tamura ◽  
Yohei Noda ◽  
Naohiko Ikuma ◽  
...  
Keyword(s):  
Electric Fields ◽  
Crystalline Phase ◽  
Liquid Crystalline ◽  
Nitroxide Radical ◽  
Liquid Crystalline Phase
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