As an increasingly common, non-radioactive alternative, CAT expression is quantified by an ELISA via immunological detection of the CAT enzyme which has been expressed.
The prokaryotic -galactosidase naturally catalyzes the hydrolysis of -galactosides (e.g. lactose). However, the use of non-physiological substrates also enables the quantification of -galactosidase activity in lysates of transfected cells via spectrophotometry (e.g. with 0-nitrophenyl--D-galactoside = ONPG), fluorometry (e.g. with a 4-methyl-umbelliferyl--galactopyranoside compound = MUG) or via chemiluminescence. Detection by chemiluminescence (e.g. with 1.2 dioxetan-galactopyranoside derivatives) is 1001,000 times more sensitive than the other two detection methods, and thus even more sensitive than the luciferase assay (see below). A major advantage of this system is the fact that -galactosidase activity can also be measured in situ.
The -galactosidase reporter gene is often co-transfected together with other reporter systems as an internal control. The -galactosidase activities can be used to compare and standardize different transfection experiments (e.g. luciferase assays).
Human Growth Hormone (hGH)
With the human Growth Hormone (hGH) reporter system in contrast
to most other systems the reporter protein is secreted into the
culture medium by the transfected cells. This means that cell lysis is
not necessary for quantifying the reporter protein. Detection of the secreted
hGH is usu