What about the hydolases ? How do they work and where do they come from ? Why do we use hydrolases ?

These enzymes have features that make them attractive as reporters. They are known to be relatively stable, exhibit activity under different conditions (e.g. pH and temperature), and catalyze the cleavage of various colorimetric and fluorescent substrates, which is ideal for visual screening (Kiernan, 2007).

LacZ : beta-galactosidase

PhoA : Alkaline phosphatase

Aes : Acetyl esterase

The acetyl-esterase Aes from "Escherichia coli" is a homodimeric enzyme, that is involved in the regulation of the Maltose operon (Joly et al., 2002). Aes belongs to the hormone-sensitive lipase (HSL) group of the esterase/lipase superfamily, and it catalyses the hydrolysis of p-nitrophenyl esters of fatty acids, preferring substrates with acyl chains of less than 8 carbons (Kanaya et al., 1998). In addition, it is able to hydrolyze triacetylglycerol (triacetin) and tributyrylglycerol (tributyrin), but not trioleylglycerol (triolein) or cholesterol oleate. This enzyme displays an optimal temperature at 65 degrees C, depicting a specific activity of 250 U/mg using pNP-butanoate as substrate, but a low half-life at the same temperature (t_1/2 of inactivation=5 min) (Farias et al., 2007).

Nagz : Glycoside hydrolase

GusA : β-glucuronidase

The E. coli β-glucuronidase (GusA) is a tetrameric enzyme that hydrolyzes a wide variety of β-glucuronides (e.g. 6-chloro-3-indolyl-beta-D-glucuronide-cycloheylammonium salt). β-glucuronidase has no cofactors, nor any ionic requirements. The enzyme can tolerate a wide range of pH, with an optimum between 5.0 and 7.8, and it is reasonably resistant to thermal inactivation with a half-life at 55 about two hours (Jefferson, 1995).