Method for testing or screening for an enzyme of interest

A method for testing an enzyme of interest or screening a library of polypeptides for an enzyme of interest comprising measuring the colour of a second dye, wherein the enzyme of interest or library of polypeptides has been contacted with a solid media in the presence of a first substrate, one or more other enzymes and a first dye, and wherein a product of the chemical reaction between an enzyme of interest and the first substrate is a substrate for one of the other enzymes, and wherein the first dye is a substrate for one of the other enzymes, and wherein the product of the chemical reaction between the first dye and one of the other enzyme is a second dye, and wherein the colour of the first dye is different from the colour of the second dye.

A method for testing a host cell or screening a library of host cells for expression of an enzyme of interest comprising measuring the colour of a second dye, wherein the host cell or library of host cells has been cultivated on or in a solid media in the presence of a first substrate, one or more other enzymes and a first dye, and wherein a product of the chemical reaction between the enzyme of interest and the first substrate is a substrate for one of the other enzymes, and wherein the first dye is a substrate for one of the other enzymes, and wherein the product of the chemical reaction between the first dye and one of the other enzyme is a second dye, and wherein the colour of the first dye is different from the colour of the second dye.