Limulus clotting factor overbar C (, ''factor C'', ''limulus factor C'') is an

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

. This enzyme catalyses the following

chemical reaction A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...

: Selective cleavage of -Arg¹⁰³-Ser- and -Ile¹²⁴-Ile- bonds in limulus clotting factor B to form ''factor overbar B''. : Cleavage of -Pro-Arg- bonds in synthetic substrates This enzyme is isolated from the

hemocyte A blood cell (also called a hematopoietic cell, hemocyte, or hematocyte) is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes), ...

granules of the

horseshoe crab Horseshoe crabs are arthropods of the family Limulidae and the only surviving xiphosurans. Despite their name, they are not true crabs or even crustaceans; they are chelicerates, more closely related to arachnids like spiders, ticks, and scor ...

Limulus ''Limulus'' is a genus of horseshoe crab, with one extant species, the Atlantic horseshoe crab (''Limulus polyphemus''). One fossil species is currently assigned to the genus though several other species have been named, which have since been a ...

and

Tachypleus ''Tachypleus'' is a genus of south, southeast and east Asian horseshoe crabs in the family Limulidae. Species There are two extant (living) species: * '' Tachypleus gigas'' (Müller, 1785) * '' Tachypleus tridentatus'' ( Leach, 1819) And two ...

, where it serves as a LPS endotoxin-sensitive

trypsin Trypsin is an enzyme in the first section of the small intestine that starts the digestion of protein molecules by cutting long chains of amino acids into smaller pieces. It is a serine protease from the PA clan superfamily, found in the dig ...

type

serine protease Serine proteases (or serine endopeptidases) are enzymes that cleave peptide bonds in proteins. Serine serves as the nucleophilic amino acid at the (enzyme's) active site. They are found ubiquitously in both eukaryotes and prokaryotes. Serin ...

to protect the

organism An organism is any life, living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have be ...

from

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

l infection, initiating a cascade leading to coagulin formation. From the N-terminus to the C-terminus, the domains are: * EGF-like domain * 3 Sushi domains * one LCCL domain and one

C-type lectin A C-type lectin (CLEC) is a type of carbohydrate-binding protein known as a lectin. The C-type designation is from their requirement for calcium for binding. Proteins that contain C-type lectin domains have a diverse range of functions including c ...

domain * 2 more Sushi domains * a trypsin domain This enzyme is useful in

Limulus amebocyte lysate Limulus amebocyte lysate (LAL) is an aqueous extract of motile blood cells (amebocytes) from the Atlantic horseshoe crab ''Limulus polyphemus''. LAL reacts with bacterial endotoxins such as lipopolysaccharides (LPS), which are components of the b ...

as the endotoxin-detecting element. It can be produced recombinantly.

References

External links

* {{Portal bar, Biology, border=no EC 3.4.21