Protein stability catalytic activity

The LB technique was chosen for covering the spheres because it was shown to provide enhanced thermal stability of many types of proteins in deposited layers (Nicolini et al. 1993, Erokhin et al. 1995, Antolini et al. 1995), which no other technique is able to achieve. Since only the upper protein layer is involved in the catalytic activity, no special attention was paid to check whether the deposited layer is a monolayer or multilayer. However, the samples were thoroughly washed to remove protein molecnles not bound covalently to the sphere surface, since during the functional test these molecules could contribute to the measured apparent catalytic activity. 

When supported complexes are the catalysts, two types of ionic solid were used zeolites and clays. The structures of these solids (microporous and lamellar respectively) help to improve the stability of the complex catalyst under the reaction conditions by preventing the catalytic species from undergoing dimerization or aggregation, both phenomena which are known to be deactivating. In some cases, the pore walls can tune the selectivity of the reaction by steric effects. The strong similarities of zeolites with the protein portion of natural enzymes was emphasized by Herron.20 The protein protects the active site from side reactions, sieves the substrate molecules, and provides a stereochemically demanding void. Metal complexes have been encapsulated in zeolites, successfully mimicking metalloenzymes for oxidation reactions. Two methods of synthesis of such encapsulated/intercalated complexes have been tested, as follows. 

The use of alkali and alkaline earth group metal ions, especially those of sodium, potassium, magnesium, and calcium, for maintenance of electrolyte balance and for signaling and promotion of enzyme activity and protein function are not discussed in this text. Many of these ions, used for signaling purposes in the exciting area of neuroscience, are of great interest. In ribozymes, RNAs with catalytic activity, solvated magnesium ions stabilize complex secondary and tertiary molecular structure. Telomeres, sequences of DNA at the ends of chromosomes that are implicated in cell death or immortalization, require potassium ions for structural stabilization. 

Nyabi et al. (162) demonstrated that PSs with mutated Asp residues are catalyti-cally inactive. Unexpectedly, these mutated PSs are still partially processed into amino- and carboxy-terminal fragments by a presenilinase-like activity and are able to rescue PEN2 expression and nicastrin glycosylation, and then they become incorporated into large 440-kDa complexes, demonstrating that the catalytic activity of PS and its other functions in the generation, stabilization, and transport of the y-secretase complex can be separated and extends the concept that PSs are multifunctional proteins (162). 

The protein(s) is relatively unstable at its true pHopt, and this lack of stability has not been corrected in the pH-activity plot. Thus, the observed pHopt is a compromise of the effect of pH on both catalytic activity (under the assay conditions) and protein denaturation and/or conformation. 

In addition to the DCTAE/DDTAV motifs, a highly conserved repetitive strand turn motif rich in aromatic amino acids (the QW motif) occurs in all OSCs and SCs and is repeated four to eight times (Table 3). These repeats are likely to be important for protein structure and stability and also for catalytic activity [55, 62-64]. The aromatic amino acids of the QW motif have been proposed to constitute sites of negative point charge that may interact with the intermediate cations during the cyclisation process [62]. 

---