Differences between mutant and wild-type

Determinations of wall rheological properties have shown marked differences between mutant and wild type. Extensibility (mm/g applied load) was measured as 0.11 for normals and 0.33 for slender seedlings whilst load/relaxation hysteresis values (under 10 g applied load) were respectively 3.3 X 10 and 8.4 X 10 J. Thus, there are marked differences in the apparent plasticity of the mutant cell wall, but these were abolished when measurements were made with killed tissue, suggesting that the differences were mediated by dynamic wall-based processes. 

The slow pace of progress toward understanding how and why SODl mutants are toxic to nxitor neurons is due to the fact dmt significant differences between mutants and wild-type enzyme have been very difScult to uncover. All of the ALS-associated SODl mutants which don t have active site mutations— and have dieir full con lement of both copper and zinc—have physical, clremical, and enzymatic properties tbich are virtually identical to d-type... 

The membrane potential depolarization in pmal mutants could be explained if the mutant enzymes were less active in pumping protons across the membrane. This notion was supported by kinetic studies on ATP hydrolysis by these enzymes that showed small but significant decreases in Vmax (15). However, a dilemma arose when whole cell medium acidification experiments were performed, which reflect the action of the H+-ATPase in vivo. The rate of glucose-induced proton efflux by pmal mutant cells was found to be considerably better than that of wild-type cells (Figure 2). Only when high external K+ was included in the medium to minimize differences in membrane potential between mutant and wild-type cells did the activity of the... 

Even mutants which have been shown to have lowered affinity for zinc will still bind it quite well in the absence of conqietitiotL Only when available zinc became limiting intracellularly would the differences in zinc binding affinity between mutants and wild-type enzyme make the mutants more likely to exist in a zinc-deficient form. 

In this chapter, we describe a protocol for the systematic perturbation of patient-derived cell lines using small-molecule probes, which is both scalable to high-throughput workflow and generalizable to a variety of assays. In the protocol presented here, multiple patient-derived lymphoblastoid cell lines either mutant or wild type at a defined genetic locus (e.g., HNF4a) are perturbed by an annotated chemical library. After sufficient incubation, cells are subjected to a phenotypic assay, in this case a luminescence-based readout of cellular ATP content, that aims to quantify the effect of compounds on oxidative phosphorylation, viability, or other relevant traits. The effect of each compound is expressed as a metric that reflects the difference in compound-induced phenotypes between mutant and wild-type cells. These ratios are then... 

The catalytic asymmetry of heterodimers was used to show that the wild-type enzyme is asymmetrical in solution. The enzyme is frozen into two populations 50% are active in one subunit and 50% in the other. For example (Figure 15.20), heterodimers containing Asn-45 on one subunit form 0.5 mol of Tyr-AMP per mole of dimer rapidly at wild-type rate (ty2 20 ms) and a further 0.5 mol four orders of magnitude more slowly ( 1/2 = 200 s) at the rate expected for mutant. If the half-of-the-sites activity were induced by the formation of the first mole of tyrosyl adenylate, then the wild-type site would be the one that is occupied. Because this does not happen, there must be frozen-in asymmetry that is randomly distributed between active wild-type subunit/inactive mutant and inactive wild-type site/active mutant. Any interconversion of active and inactive subunits is on a much slower time scale than the half-life of several minutes required for formation of E Tyr-AMP at the mutated site (Asn-45). There is no evidence that the behavior of the heterodimers is different from that of wild-type enzyme. 

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