5-Bromo-4-chloro-3-indolyl phosphate (BCIP, X-phosphate, XP) is an artificial chromogenic
substrate
Substrate may refer to:
Physical layers
*Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached
** Substrate (locomotion), the surface over which an organism lo ...
used for the sensitive
colorimetric
Colorimetry is "the science and technology used to quantify and describe physically the human color perception".
It is similar to spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color ...
detection of
alkaline phosphatase activity. It is, for example, used in
immunoblotting
The western blot (sometimes called the protein immunoblot), or western blotting, is a widely used analytical technique in molecular biology and immunogenetics to detect specific proteins in a sample of tissue homogenate or extract. Besides detecti ...
,
in situ hybridization
''In situ'' hybridization (ISH) is a type of hybridization that uses a labeled complementary DNA, RNA or modified nucleic acids strand (i.e., probe) to localize a specific DNA or RNA sequence in a portion or section of tissue (''in situ'') or ...
, and
immunohistochemistry
Immunohistochemistry (IHC) is the most common application of immunostaining. It involves the process of selectively identifying antigens (proteins) in cells of a tissue section by exploiting the principle of antibodies binding specifically to a ...
, often in combination with
nitro blue tetrazolium chloride
Nitro blue tetrazolium is a chemical compound composed of two tetrazole moieties. It is used in immunology for sensitive detection of alkaline phosphatase (with BCIP). NBT serves as the oxidant and BCIP is the AP- substrate (and gives also dark b ...
(NBT).
[
Alkaline phosphatase hydrolyses BCIP to 5-bromo-4-chloro-3-indoxylphosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phosph ...]
5-bromo-4-chloro-3-indoxyl is oxidized by atmospheric oxygen to form the blue dye 5,5′-dibromo-4,4′-dichloro-indigo. It is also oxidized by nitroblue tetrazolium (NBT), which forms an insoluble dark blue diformazan precipitate after reduction. Alkaline phosphatase is commonly conjugated to