2 research outputs found

    Policymaking Under Pressure: The Perils of Incremental Responses to Climate Change

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    Federal policymakers' reluctance to enact a comprehensive climate change policy during the past decade has coincided with increased awareness of the inevitability and severity of the problems from global climate change. Thus, it is no surprise that piecemeal, sub-federal policies have garnered considerable support. Bolstered by the political science literature on the promise of incrementalism and democratic experimentalism, many proponents of climate change action favor incremental steps in the hope that they will improve the environment or at least serve as a basis for more comprehensive policies. Against this hopeful view, we explain why ad hoc responses to climate change may well be no better than, and possibly will be worse than, no action at all. Incremental climate change policies can give rise to predictable and nontrivial problems, such as non-effect, leakage, climate side effects, other side effects, lock-in, and lulling. Such problems not only can undermine the interim policies themselves but also may delay the adoption of a more comprehensive climate change policy. We present an upstream cap-and-trade policy as one such comprehensive alternative, showing how it would prove less susceptible to the kinds of policy failures that afflict incremental policies. Only by resisting the pressures to act immediately, and investing the necessary time and resources to craft a comprehensive solution, will environmental policymakers be able to guard against the perils that afflict ad hoc policymaking.

    Methylmalonate-semialdehyde Dehydrogenase from Bacillus subtilis: SUBSTRATE SPECIFICITY AND COENZYME A BINDING*

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    Methylmalonate-semialdehyde dehydrogenase (MSDH) belongs to the CoA-dependent aldehyde dehydrogenase subfamily. It catalyzes the NAD-dependent oxidation of methylmalonate semialdehyde (MMSA) to propionyl-CoA via the acylation and deacylation steps. MSDH is the only member of the aldehyde dehydrogenase superfamily that catalyzes a β-decarboxylation process in the deacylation step. Recently, we demonstrated that the β-decarboxylation is rate-limiting and occurs before CoA attack on the thiopropionyl enzyme intermediate. Thus, this prevented determination of the transthioesterification kinetic parameters. Here, we have addressed two key aspects of the mechanism as follows: 1) the molecular basis for recognition of the carboxylate of MMSA; and 2) how CoA binding modulates its reactivity. We substituted two invariant arginines, Arg-124 and Arg-301, by Leu. The second-order rate constant for the acylation step for both mutants was decreased by at least 50-fold, indicating that both arginines are essential for efficient MMSA binding through interactions with the carboxylate group. To gain insight into the transthioesterification, we substituted MMSA with propionaldehyde, as both substrates lead to the same thiopropionyl enzyme intermediate. This allowed us to show the following: 1) the pKapp of CoA decreases by ∼3 units upon binding to MSDH in the deacylation step; and 2) the catalytic efficiency of the transthioesterification is increased by at least 104-fold relative to a chemical model. Moreover, we observed binding of CoA to the acylation complex, supporting a CoA-binding site distinct from that of NAD(H)
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