Many scientists,

these days also rely upon a gel scanner to estimate protein in a given sample by running a SDS-PAGE. The few features of these methods are sometimes less clearly taken into account than desirable. 1. Most of the protein estimation methods rely upon the color-generating response of the protein during a chemical reaction (e.g. Biuret, Lowry or BCA methods) (Walker, 2002) or physical BIRB 796 interaction with a compound (e.g. frequently used dye-binding assay) (Bradford, 1976). Different proteins respond in a quantitatively different way. In this respect, Biuret is an exception as it gives relatively uniform response for most of proteins. This is much less sensitive than other methods (Scopes, 1994). However, most of the industrial enzymes contain a good amount of protein/g, so Biuret actually may be a good option. Most

of the other methods give the relative protein concentration. For example, it is a general practice to say that a particular protein estimation method was employed and BSA was used for a standard curve. The color-generating buy MG-132 response by the protein can be very significantly different from BSA. This is not a cause of worry as we mostly track change in protein concentration during any operation/process. For example, during protein purification, we are only concerned with fold purification starting with a crude preparation. So, the relative protein concentration value should be good enough. However, when we calculate the amount of protein expressed and obtained as inclusion bodies ( Garcia-Fruitos et al., 2012), we tend to overlook that we are not talking of absolute protein concentration. The amounts of an enzyme present in a given sample, reaction system or bioreactor is obviously an important parameter. If the reaction condition Amylase obeys Michaelis–Menten kinetics, it is implied that [E]«[S]. Ideally, if the amount of enzyme is increased x times, the initial rate is expected to increase x times. In reality, it may not happen. The plot of velocity vs. [E] curve may have an increasing slope (display a lag period or a slow phase) if: (a) The oligomeric form of an enzyme has higher activity or

if the subunits of the enzyme dissociate in dilute solutions. On the other hand, the velocity vs. [E] curve may have a decreasing slope (i.e. the velocity slows down with increase in [E]) because: (i) The enzyme has a tendency to aggregate. These aggregates may be soluble. So, no visible precipitation is observed. Earlier, it was believed that extensive aggregation requires unfolding of the protein chain. Now, there is growing evidence that even “native-like structures” may aggregate (Bemporad et al., 2012). Intrinsically disordered proteins (IDP), of course, constitute an extreme case in this regard (Uversky, 2011). Aggregates are generally inactive although recently alpha chymotrypsin subjected to three-phase partitioning (TPP) (Rather et al.