Thiol groups NADH dehydrogenases

Figure 2. Illustration of the importance of the choice of reaction conditions on the determination of initial velocity. Shown are four conditions applied to examine the rate behavior of Escherichia coli NAD+-dependent coenzyme A-linked aldehyde dehydrogenase (Reaction NAD+ + CoA-SH + Acetaldehyde = NADH + Acetyl-S-CoA + H+). All assay mixtures contained enzyme, 0.5 mM NAD+, 8 /jlW CoA-SFI, 16 mM acetaldehyde, and 22.5 mM Tris buffer at pFI 8.1. (a) Time-course observed when enzyme was added to the standard assay (b) time-course observed when enzyme was added to standard assay augmented with 10 mM 2-mercaptoethanol (c) time-course observed when enzyme was first preincubated for 15 min with 8 /jlW CoA-SH, 16 mM acetaldehyde, 10 mM 2-mercaptoethanol, and 22.5 mM Tris buffer at pH 8.1, and the reaction was initiated by addition of NAD+ (d) time-course observed when enzyme was preincubated with lOmM 2-mercaptoethanol for 15 min andthen addedtostandard assay augmented with 10 mM 2-mercaptoethanol. The data are most compatible with the idea that the enzyme has an active-site thiol group that must be reduced to express full catalytic activity during assay.

V at pH 7.0 it is not considered very reactive, except e.g. with ascorbate and with NADH bound to lactate dehydrogenase and with the thiol group of cysteine, as shown by the inactivation of papain... 

The literature confirms that attempts to clarify the mechanism of silver nanoparticle action against bacteria, viruses, and fungi have been taken. One of the most common mechanisms of nanosilver antibacterial activity is based on its natural affinity for bonding with a thiol group present in cysteine, which is a protein building material of bacterial cell walls. Consequently, the enzymatic function of the proteins is disturbed and the cellular respiration chain is interrupted. At the same time other enzymes such as NADH and succinate dehydrogenase are destroyed (Park et al., 2009). 

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