Proteins enzyme kinetics

The Influence of Environmental Factors on Enzyme Kinetics. Because enzymes are proteins, they are unusually sensitive to changes in their environment. This is true not only with regard to variations in inhibitor concentrations, but also with respect to variations in pH and temperature. Most enzymes are efficient catalysts only within relatively narrow ranges of pH and temperature. 

The question arises as to whether comparisons with protein enzymes are justified. In other words, what can ribozymes really do An important parameter for measuring the efficiency of enzymes is the value of kc-JK. This quotient is derived from the values of two important kinetic parameters kc-Al is a rate constant, also called turnover number, and measures the number of substrate molecules which are converted by one enzyme molecule per unit time (at substrate saturation of the enzyme). Km is the Michaelis-Menten constant it corresponds to the substrate concentration at which the rate of reaction is half its maximum. 

Thus we will consider only systems where there is experimental evidence for both catalysis with turnover and the initial binding interaction, generally in the shape of saturation kinetics (and reserve the use of the unmodified term enzyme specifically to mean a protein enzyme). 

In liver microsomes, the formation of 1-, 2-, and 3-hexanol from -hexane was best described kinetically by a 2-enzyme system, while for lung microsomes, single-enzyme kinetics were indicated for each metabolite. For conversion to 1-hexanol, apparent Km values were 0.4 and 300 M, and Vmax values were 0.09 and 1.2 nmol/mg protein/min, respectively. For conversion to 2-hexanol, apparent Km values were 6 and 1,100 M, and Vmax values were 1 and 4.6 nmol/mg protein/min respectively. Insufficient information was available to estimate the high-affinity activity for 3-hexanol, the low-affinity activity had an apparent Km of 290 M and a Vmax of 0.5 nmol/mg protein/min. In the lung, Km values were 9,... 

It is of interest in this connection that Steam,26 in a discussion of enzyme kinetics from the point of view of statistical mechanics and quantum mechanics, regards interaction between a dipole (as part of the enzyme protein) and the reacting groups of the substrate, e.g., C—0, resulting in a redistribution of charge within the C—0 bond, as a more rational mechanism of activation than the loosening of the bond by distortion. 

Proteins in vivo protein-protein interactions, protein folding kinetics, protein subunit exchange, enzyme activity assay, etc. 

Since the propensity to form adducts in chemistry is high and these adducts undergo a variety of reactions, the rate law (1.98) is quite common. This is particularly true in enzyme kinetics. In reality, these reaction schemes give biphasic first-order plots but because the first step is usually more rapid, for example between A and B in (1.101) we do not normally, nor do we need to, examine this step in the first instance. The value of A", in (1.107) obtained kinetically can sometimes be checked directly by examining the rapid preequilibrium before reaction to produce D occurs. In the reactions of Cu(I) proteins with excited Cr and Ru polypyridine complexes, it is considered that (a) and (b) schemes may be operating concurrently. 

This plot is known as a Hill plot in protein-binding chemistry and enzyme kinetics (11). Transformation of Eq. (13) also provides the relation for the mobilities ... 

In order to give a homogeneous distribution of enzyme molecules inside the membrane, it was necessary to synthesize the membrane and to incorporate the enzymes at the same time. The co-cross-linking of enzyme molecules with an inert protein appears to be a proper solution. Purely active proteic films were created by using this procedure.11-12 These artificial enzyme membranes can be used in the study of heterogeneous enzyme kinetics and for modeling biological membranes. The phenomena in the enzyme membranes can be classified in two parts. 

Our work deals with the necessity of creating kinetics laws for heterogeneous enzymology. There was a big gap between the classical enzyme kinetics in solution and highly structured biological systems. All the concepts of diffusion reaction are clear for our thick membrane but are also useful for lipid-protein membranes, even if the process of transport is not only classical diffusion. 

The sulfation of phenol and the glucuronidation of its hydroquinone metabolite were measured in human liver cytosols and microsomes, respectively. The rate of phenol sulfation varied between 0.31 and 0.92 nmol/mg protein/min this is slightly higher than the rate for mice (0.46) and lower than that for rats (1.20). The rate of hydroquinone glucuronidation was between 0.10 and 0.28 mnol/mg protein/min, slightly higher than that for rats (0.08) and lower than that for mice (0.22). These enzyme-kinetic data were subsequently used to simulate phenol metabolism in mice, rats and humans in vivo, using a com-partmental pharmacokinetic model with benzene as phenol precursor (Seaton et al., 1995). 

Purification and Enzyme Kinetic Analysis of Variant GST-pi Proteins... 

---