Pumiliotoxins (PTXs), are one of several toxins found in the skin of

poison dart frog Poison dart frog (also known as dart-poison frog, poison frog or formerly known as poison arrow frog) is the common name of a group of frogs in the family Dendrobatidae which are native to tropical Central and South America. These species are ...

s. The frog species, P. bibronii also produces PTXs to deter predators. Closely related, though more toxic, are

allopumiliotoxin Allopumiliotoxins are a structural division in the pumiliotoxin-A class of alkaloids. The compounds of the pumiliotoxin-A class are primarily found in the skins of frogs, toads, and other amphibians and are used as a chemical defense mechanism to ...

s, (aPTXs). Other toxins found in the skin of poison frogs include decahydroquinolines (DHQs), izidines, coccinellines, and spiro

pyrrolizidine alkaloid Pyrrolizidine alkaloids (PAs), sometimes referred to as necine bases, are a group of naturally occurring alkaloids based on the structure of pyrrolizidine. Their use dates back centuries and is intertwined with the discovery, understanding, and e ...

s. Pumiliotoxins are poisonous in high concentrations. Pumiliotoxins are much weaker than

batrachotoxin Batrachotoxin (BTX) is an extremely potent cardiotoxic and neurotoxic steroidal alkaloid found in certain species of beetles, birds, and frogs. The name is from the Greek word . Structurally-related chemical compounds are often referred to collec ...

s, ranging between 100 and 1000 times less poisonous.

Structure

The different divisions of compounds in the pumiliotoxin-A class arise from differences in the carbon backbone and/or the substituents attached to it. The difference between allopumiliotoxins and pumiliotoxins occurs at the 7 position. At this position, pumiliotoxins have a hydrogen whereas allopumiliotoxins have a

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

substituent. Both have

methyl In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula (whereas normal methane has the formula ). In formulas, the group is often abbreviated as ...

and hydroxyl groups at the C-8 position. Homopumiliotoxins contain a

quinolizidine Quinolizidine (norlupinane, octahydro-2''H''-quinolizine) is a nitrogen-containing heterocyclic compound. Some alkaloids (e.g. cytisine and sparteine) are derivatives of quinolizidine. Quinolizidine alkaloids Quinolizidine alkaloids, such as ...

ring in the place of the indolizidine ring and methyl and hydroxyl groups at its C-9 position. All three contain an alkylidenyl side-chain.Jain, P.; Garraffo, H. M.; Spande, T. F.; Yeh, H. J. C.; Daly, J. W. J. Nat. Prod. 1995, 58, 100-104.

Nomenclature

Pumiliotoxins (or their analogs, allopumiliotoxins and homopumiliotoxins) are named by their class followed by their

molecular weight A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

Isomers In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the existence or possibili ...

are differentiated by a letter after the number. For example, allopumiliotoxin 339A is an allopumiliotoxin with a molecular weight of 339 g/mol, with an axially oriented hydroxyl group at the 7-position in the

indolizidine Indolizidine is a heterocyclic chemical compound that forms the central core of the indolizidine alkaloids such as swainsonine and castanospermine. See also * Indole * Indolizine * Tryptophan * Tryptamine Tryptamine is an indolamine metaboli ...

nucleus that differentiates it from allopumiliotoxin 339B.Aoyagi, S.; Wang, T. C.; Kibayashi, C. J. Am. Chem. Soc. 1993, 115, 11393-11409. A (+) or (−) sign preceding the name of a pumiliotoxin refers to the compound’s rotation of polarized light, with clockwise rotation (dextrorotatation) denoted with (+) and counterclockwise rotation (levorotation) denoted with (-).

Accumulation

Frogs obtain pumiliotoxins from their diet in

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

s; frogs raised in terrariums in the absence of their natural diet do not produce alkaloids. The toxins are then accumulated in secretory granular glands of the skin of the frog. Some frog species of the Dendrobates genera can convert pumiliotoxins into allopumiliotoxins by a hydroxylase. Only one of the

enantiomers In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...

can be hydroxylated to this more potent form of the toxin. The lack of pumiliotoxin 251D in eggs and tadpoles show that the toxin is not passed over from adult frogs to their offspring. The tadpoles are therefore not readily protected from predators.

Physiological Effects

Pumiliotoxins and allopumiliotoxins are generally positive modulators of voltage gated sodium channels and increase the strength of heart contraction. One exception is

pumiliotoxin 251D Pumiliotoxin 251D is a toxic organic compound. It is found in the skin of poison frogs from the genera '' Dendrobates'', ''Epipedobates'', '' Minyobates'', and ''Phyllobates'' and toads from the genus '' Melanophryniscus''. Its name comes from th ...

, which blocks the flux of Na⁺ ions and increases the permeability of K⁺ ions.

References

External links

Poison Dart Frogs

Indolizidine alkaloids Neurotoxins {{Dendrobatidae-stub