Calculation of Excess Stability Functions of Four Binary Alloys

The thermodynamic model based on cluster of two atoms is considered with the view to obtaining Scc(0) and the excess stability function of Scc(0). Concentration-concentration fluctuation; Scc(0) of four binary molten alloys was calculated. The thermodynamic properties of these alloys are evaluated based on cluster of two atoms (A & B) or (B & A). Each system has the view of obtaining concentration-concentration fluctuation; Scc(0) enumerating the low-order atomic correlation in the nearest neighbour shell of liquid binary alloys.The highlights of excess stability functions(ES) of Scc(0) of these alloys were reported. The values of Scc(0) for all these alloys are higher than the ideal solution values. The values of Scc(0) for Bi-Cd alloy is close to the ideal Scc (0). The indication of the excess stability of Scc(0) for some alloys is in support of homocoordination. The Scc(0) and excess stability function of Scc (0) for the four alloys are presented. Keywords: Concentration-concentration fluctuation, Excess stability function, Ordering energy.

Substrate inhibition imposes fitness penalty at high protein stability

Proteins are only moderately stable. It has long been debated whether this narrow range of stabilities is solely a result of neutral drift toward lower stability or purifying selection against excess stability—for which no experimental evidence was found so far—is also at work. Here, we show that mutations outside the active site in the essential Escherichia coli enzyme adenylate kinase (Adk) result in a stability-dependent increase in substrate inhibition by AMP, thereby impairing overall enzyme activity at high stability. Such inhibition caused substantial fitness defects not only in the presence of excess substrate but also under physiological conditions. In the latter case, substrate inhibition caused differential accumulation of AMP in the stationary phase for the inhibition-prone mutants. Furthermore, we show that changes in flux through Adk could accurately describe the variation in fitness effects. Taken together, these data suggest that selection against substrate inhibition and hence excess stability may be an important factor determining stability observed for modern-day Adk.

Substrate inhibition imposes fitness penalty at high protein stability

Proteins are only moderately stable. It has long been debated whether this narrow range of stabilities is solely a result of neutral drift towards lower stability or purifying selection against excess stability is also at work — for which no experimental evidence was found so far. Here we show that mutations outside the active site in the essential E. coli enzyme adenylate kinase result in stability-dependent increase in substrate inhibition by AMP, thereby impairing overall enzyme activity at high stability. Such inhibition caused substantial fitness defects not only in the presence of excess substrate but also under physiological conditions. In the latter case, substrate inhibition caused differential accumulation of AMP in the stationary phase for the inhibition prone mutants. Further, we show that changes in flux through Adk could accurately describe the variation in fitness effects. Taken together, these data suggest that selection against substrate inhibition and hence excess stability may have resulted in a narrow range of optimal stability observed for modern proteins.