Lipid-modified enzyme properties

The modification of enzyme by attaching ions or molecules is a suitable way for providing it with useful fimctions. For example, the use of modifiers such as polyethylene glycol (PEG) (7,2) and synthetic lipids (i) enhances the affinity for hydrophobic environments. PEG-modified enzymes are soluble and active in various organic solvents as well as aqueous solutions (7,2). Lipid-modified enzymes are insoluble in aqueous solutions, but show catal c activities in both aqueous and organic media (i). These unique properties lead us to apply PEG- and lipid-modified enzymes in the construction of enzyme electrodes. 

Properties of Lipid-Modified GOD. The GOD content in the lyophilized product of lipid-modified GOD was calculated to be 33%. The modified enzyme was soluble in nonpolar organic solvents, such as benzene and chlorofonn. Tire GOD activity of the modified enzyme was 38 U mg -solid, which corresponds to 115 U mg l-GOD. This shows that file enzyme activity does not decrease during the modification process and that the enzyme substrates, glucose and o gen permeate easily into the lipid layer on the GOD molecule to reach active site. 

Enzymes are proteins with catalytic properties. The catalytic properties are quite specific, which makes enzymes useful in analytical studies. Some enzymes consist only of protein, but most enzymes contain additional nonprotein components such as carbohydrates, lipids, metals, phosphates, or some other organic moiety. The complete enzyme is called holoenzyme the protein part, apoenzyme and the nonprotein part, cofactor. The compound that is being converted in an enzymic reaction is called substrate. In an enzyme reaction, the substrate combines with the holoenzyme and is released in a modified form, as indicated in Figure 10-1. An enzyme reaction, therefore, involves the following equations ... 

It is not clear why LA and none of the saturated fatty acids that were studied disrupted endothelial barrier function. The injurious effects of LA on cultured endothelial cells may be mediated, in part, by the induction of peroxisomes and, thus, by excessive hydrogen peroxide formation. In addition, enrichment of endothelial lipids with selective fatty acids can modify specific cellular lipid pools and alter the morphology of cultured cell monolayers. Such fatty acid-mediated compositional changes may be sufficient to alter membrane properties, e.g., fluidity and activities of membrane-bound enzymes. One may speculate from these and other data that high dietary intakes of certain unsaturated fatty acids, such as LA, might not be entirely safe. 

Outline of the cellular events that result in the activation of protein kinase C (PKC). The enzyme apparently exists in at least two states. Recent sequence work indicates that it has a Ca -binding site of the EF-hand type. When no Ca " ion is bound, and when the concentration of diacylglycerol (DG) in the inner layer of the plasma membrane is low, the kinase exists in a low-activity form, possibly dissociated from the membrane. When a hormone binds to a plasma-membrane receptor (R), cleavage of phosphoinositol into 1,4,5-1P3 and DG is induced. The latter lipid may bind to and activate the calcium-loaded form of PKC. The active form of protein kinase C will now phosphorylate other cytoplasmic proteins, and in this way modify their biochemical properties. R = receptor PL-C = phospholipase C G = a GTP-binding protein that is assumed to act as an intermediary between the receptor and the membrane bound PL-C. 

Both organisms acquire host lipid, albeit through different paths, possess signifieant pathways to modify these lipids, and have enzymic activities, for example phospholipases or transporters with unusual properties, which are able to facilitate the process. The malaria parasite, sequestered within the host... 

The use of electrodes modified with immobilized redox-active molecules provides a simple methodology by which to study the ultrathin film electrochemistry of water-insoluble redox-active molecules, encouraging the application of such techniques to biomimetic membranes in aqueous media. It is of interest to use monolayer and LB films of enzymes, proteins, and antibodies as biosensors or biomolecular switches because of their high sensitivity for their substrates and antigens, respectively. The formation of thin fullerene films including fullerene-lipid hybrid and fullerene-lipid composite bilayer membranes is of interest both from a fundamental and practical application point of view. Multiwalled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) are novel nanomaterials that have remarkable electronic, mechanical, and thermal properties, and specific functions. Soluble carbon nanotubes in aqueous and organic systems are of interest since their study allows the... 

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