Snake venom

Snake venom is a highly toxic saliva containing zootoxins that facilitates in the immobilization and digestion of prey. This also provides defense against threats. Snake venom is usually injected by unique fangs during a bite, though some species are also able to spit venom.
The venom glands that secrete zootoxins are a modification of the parotid salivary glands found in other vertebrates and are usually located on each side of the head, below and behind the eye, and enclosed in a muscular sheath. The venom is stored in large glands called alveoli before being conveyed by a duct to the base of channeled or tubular fangs through which it is ejected.
Venom contains more than 20 different compounds, which are mostly proteins and polypeptides. The complex mixture of proteins, enzymes, and various other substances has toxic and lethal properties. Venom serves to immobilize prey. Enzymes in venom play an important role in the digestion of prey, and various other substances are responsible for important but non-lethal biological effects. Some of the proteins in snake venom have very specific effects on various biological functions, including blood coagulation, blood pressure regulation, and transmission of nerve or muscle impulses. These venoms have been studied and developed for use as pharmacological or diagnostic tools, and even drugs.

Chemistry

constitute 90-95% of venom's dry weight and are responsible for almost all of its biological effects. The hundreds, even thousands, of proteins found in venom include toxins, neurotoxins in particular, as well as nontoxic proteins, and many enzymes, especially hydrolytic ones. Enzymes make up 80-90% of viperid and 25-70% of elapid venoms, including digestive hydrolases, L-amino-acid oxidase, phospholipases, thrombin-like pro-coagulant, and kallikrein-like serine proteases and metalloproteinases, which damage vascular endothelium. Polypeptide toxins include cytotoxins, cardiotoxins, and postsynaptic neurotoxins, which bind to acetylcholine receptors at neuromuscular junctions. Compounds with low molecular weight include metals, peptides, lipids, nucleosides, carbohydrates, amines, and oligopeptides, which inhibit angiotensin-converting enzyme and potentiate bradykinin. Inter- and intra-species variation in venom chemical composition is geographical and ontogenic. Phosphodiesterases interfere with the prey's cardiac system, mainly to lower the blood pressure. Phospholipase A2 causes hemolysis by lysing the phospholipid cell membranes of red blood cells. Amino acid oxidases and proteases are used for digestion. Amino acid oxidase also triggers some other enzymes and is responsible for the yellow colour of the venom of some species. Hyaluronidase increases tissue permeability to accelerate the absorption of other enzymes into tissues. Some snake venoms carry fasciculins, like the mambas, which inhibit cholinesterase to make the prey lose muscle control.

Type	Name	Origin
Oxidoreductases	lactate dehydrogenase	Elapidae
	L-amino-acid oxidase	All species
	Catalase	All species
Transferases	Alanine amino transferase
Hydrolases	Phospholipase A2	All species
	Lysophospholipase	Elapidae, Viperidae
	Acetylcholinesterase	Elapidae
	Alkaline phosphatase	Bothrops atrox
	Acid phosphatase	Deinagkistrodon acutus
	5'-nucleotidase	All species
	Phosphodiesterase	All species
	Deoxyribonuclease	All species
	Ribonuclease 1	All species
	Adenosine triphosphatase	All species
	Amylase	All species
	Hyaluronidase	All species
	NAD-Nucleotidase	All species
	Kininogenase	Viperidae
	Factor X activator	Viperidae, Crotalinae
	Heparinase	Crotalinae
	α-Fibrinogenase	Viperidae, Crotalinae
	β-Fibrinogenase	Viperidae, Crotalinae
	α-β-Fibrinogenase	Bitis gabonica
	Fibrinolytic enzyme	Crotalinae
	Prothrombin activator	Crotalinae
	Collagenase	Viperidae
	Elastase	Viperidae
Lyases	Glucosaminate ammonia-lyase

Snake toxins vary greatly in their functions. The two broad classes of toxins found in snake venoms are neurotoxins and hemotoxins. However, exceptions occur – the venom of the black-necked spitting cobra, an elapid, consists mainly of cytotoxins, while that of the Mojave rattlesnake, a viperid, is primarily neurotoxic. Both elapids and viperids may carry numerous other types of toxins.

Toxins

Neurotoxins

The beginning of a new neural impulse goes as follows:

An exchange of ions across the nerve cell membrane sends a depolarizing current towards the end of the nerve cell.
When the depolarizing current arrives at the nerve cell terminus, the neurotransmitter acetylcholine, which is held in vesicles, is released into the space between the two nerves. It moves across the synapse to the postsynaptic receptors.
ACh binds to the receptors and transfers the signal to the target cell, and after a short time, it's destroyed by acetylcholinesterase.
Fasciculins

Dendrotoxins

α-neurotoxins

Cytotoxins

Phospholipases

Cardiotoxins / Cytotoxins

Hemotoxins

Myotoxins

s are small, basic peptides found in rattlesnake and lizard venoms. This involves a non-enzymatic mechanism that leads to severe skeletal muscle necrosis. These peptides act very quickly, causing instantaneous paralysis to prevent prey from escaping and eventually death due to diaphragmatic paralysis.
The first myotoxin to be identified and isolated was crotamine, discovered in the 1950s by Brazilian scientist José Moura Gonçalves from the venom of tropical South American rattlesnake Crotalus durissus terrificus. Its biological actions, molecular structure and gene responsible for its synthesis were all elucidated in the last two decades.

Determining venom toxicity (LD₅₀)

Snake venom toxicity is assessed by a toxicological test called the median lethal dose, lethal dose 50%, which determines the concentration of a toxin required to kill half the members of a tested population. The potency of wild snake venom varies considerably because of assorted influences such as biophysical environment, physiological status, ecological variables, genetic variation, and other molecular and ecological evolutionary factors. This is true even for members of one species. Such variation is smaller in captive populations in laboratory settings, though it cannot be eliminated. However, studies to determine snake venom potency must be designed to minimize variability.
Several techniques have been designed to this end. One approach is to use 0.1% bovine serum albumin as a diluent in determining LD₅₀ values. It results in more accurate and consistent LD₅₀ determinations than using 0.1% saline as a diluent. For example, fraction V produces about 95% purified albumin. Saline as a diluent consistently produces widely varying LD₅₀ results for nearly all venomous snakes. It produces unpredictable variation in precipitate purity. Fraction V is structurally stable because it has seventeen disulfide bonds; it's unique in that it has the highest solubility and lowest isoelectric point of major plasma proteins. This makes it the final fraction to be precipitated from its solution. Bovine serum albumin is located in fraction V. The precipitation of albumin is done by reducing the pH to 4.8, near the pH of the proteins, and maintaining the ethanol concentration at 40%, with a protein concentration of 1%. Thus, only 1% of the original plasma remains in the fifth fraction.
When the ultimate goal of plasma processing is a purified plasma component for injection or transfusion, the plasma component must be highly pure. The first practical large-scale method of blood plasma fractionation was developed by Edwin J. Cohn during World War II. it's known as the Cohn process. This process is also known as cold ethanol fractionation, as it involves gradually increasing the concentration of ethanol in the solution at 5 °C and 3 °C. The Cohn Process exploits differences in plasma proteins properties, specifically, the high solubility and low pI of albumin. As the ethanol concentration is increased in stages from 0 to 40%, the pH declines from neutral to about 4.8, which is near the pI of albumin. At each stage, proteins are precipitated out of the solution and removed. The final precipitate is purified albumin. Several variations to this process exist, including an adapted method by Nitschmann and Kistler that uses fewer steps, and replaces centrifugation and bulk freezing with filtration and diafiltration. Some newer methods of albumin purification add additional purification steps to the Cohn process and its variations. Chromatographic albumin processing emerged in the 1980s, however, it was not widely adopted until later due to the scarity of large-scale chromatography equipment. Methods incorporating chromatography generally begin with cryo-depleted plasma undergoing buffer exchange via either diafiltration or buffer exchange chromatography, to prepare the plasma for following ion exchange chromatography steps. After ion exchange, generally purification steps and buffer exchange occur.
However, chromatographic methods began to be adopted in the 1980s. Developments were ongoing between when Cohn fractionation started emerge in 1946, and when chromatography emerged, in 1983. In 1962, the Kistler and Nistchmann process was created as a spin-off of the Cohn process. In the 1990s, the Zenalb and the CSL Albumex processes were created, which incorporated chromatography with variations. The general approach to using chromatography for plasma fractionation for albumin is: recovery of supernatant I, delipidation, anion exchange chromatography, cation exchange chromatography, and gel filtration chromatography. The recovered purified material is formulated with combinations of sodium octanoate and sodium N-acetyl tryptophanate and then subjected to viral inactivation procedures, including pasteurization at 60 °C. This is a more efficient alternative than the Cohn process because:

smooth automation and a relatively inexpensive plant was needed,
easier to sterilize equipment and maintain a good manufacturing environment
chromatographic processes are less damaging to the albumin protein
a more successful albumin result can be achieved.

Compared with the Cohn process, albumin purity increased from about 95% to 98% using chromatography, and the yield increased from about 65% to 85%. Small percentage increases make a difference in regard to sensitive measurements such as purity. The big drawback has to do with the economics. Although the method offered efficient, acquiring the necessary equipment was difficult. Large machinery is necessary, and for a long time, the lack of equipment availability limited its widespread use.