Adipokinetic hormone
Encyclopedia
Adipokinetic hormone is a short peptide hormone
that has been studied in insect
s. It is a lipid
mobilising hormone and is responsible for regulating fuel transport in the haemolymph, for redirecting energy to other processes as required by the insect. AKH was initially discovered in the desert locust Schistocerca gregaria and is generally associated with aiding flight . Early observations of locust
s showed that despite the fact that lipids are metabolised by flight muscle in order to maintain flight, which would be transported from the haemolymph, there was often still a high concentration of lipids in the haemolymph, implying that an agent may be responsible for activating lipid transport into the haemolymph and this was thought most likely to be hormonal regulation.. The hormone itself is part of a larger family, often referred to as red pigment concentrating hormones (RPCH) discovered in crustaceans and the typical makeup of hormones in this family includes a length between 8 and 10 amino acids, blocked N and C termini, phenylalanine or tyrosine at position 4 and tryptophan at position 8 . RPCH was discovered in crustaceans and shown to be involved in concentrating red pigments, for sexual displays and a variety of other reasons. The similarity between AKH and RPCH is so significant that injecting insects with RPCH induces an AKH like response and vice-versa
AKH was first purified by an English group in 1976 and the chemical structure was determined to be a peptide hormone
formed from 10 amino acids. This was the first instance where an insect peptide hormone had been identified..
Later, after AKH was identified in cockroach
es, locust AKH was inserted into a cockroach and a similar increase in lipid mobilisation was observed. Conversely, cockroach AKH led to similar activity within a locust.
AKH has become an important area of study, particularly in insect crop pests and insects that act as intermediate or vector hosts for parasites that can affect humans or agricultural animals. It is believed that AKH does not only aid flight in insects, but it has also been shown that an increase in AKH can lead to stronger immune responses in locusts . One group have performed experiments where locusts received an injection including AKH and lipopolysaccharide
(LPS) – an immune elicitor found in the cell walls of bacteria – led to a stronger immune response than locusts which only received an LPS injection . This implies that lipid mobilisation by AKH can have a variety of uses for energy dynamics within insects and may be important in a range of functions that are related to insect survival. It is now believed that parasites which infect insects may stimulate the production of AKH in order to mobilise lipids which can then be used for parasite gains.
Peptide hormone
Peptide hormones are a class of peptides that are secreted into the blood stream and have endocrine functions in living animals.Like other proteins, peptide hormones are synthesized in cells from amino acids according to an mRNA template, which is itself synthesized from a DNA template inside the...
that has been studied in insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s. It is a lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
mobilising hormone and is responsible for regulating fuel transport in the haemolymph, for redirecting energy to other processes as required by the insect. AKH was initially discovered in the desert locust Schistocerca gregaria and is generally associated with aiding flight . Early observations of locust
Locust
Locusts are the swarming phase of short-horned grasshoppers of the family Acrididae. These are species that can breed rapidly under suitable conditions and subsequently become gregarious and migratory...
s showed that despite the fact that lipids are metabolised by flight muscle in order to maintain flight, which would be transported from the haemolymph, there was often still a high concentration of lipids in the haemolymph, implying that an agent may be responsible for activating lipid transport into the haemolymph and this was thought most likely to be hormonal regulation.. The hormone itself is part of a larger family, often referred to as red pigment concentrating hormones (RPCH) discovered in crustaceans and the typical makeup of hormones in this family includes a length between 8 and 10 amino acids, blocked N and C termini, phenylalanine or tyrosine at position 4 and tryptophan at position 8 . RPCH was discovered in crustaceans and shown to be involved in concentrating red pigments, for sexual displays and a variety of other reasons. The similarity between AKH and RPCH is so significant that injecting insects with RPCH induces an AKH like response and vice-versa
AKH was first purified by an English group in 1976 and the chemical structure was determined to be a peptide hormone
Peptide hormone
Peptide hormones are a class of peptides that are secreted into the blood stream and have endocrine functions in living animals.Like other proteins, peptide hormones are synthesized in cells from amino acids according to an mRNA template, which is itself synthesized from a DNA template inside the...
formed from 10 amino acids. This was the first instance where an insect peptide hormone had been identified..
Later, after AKH was identified in cockroach
Cockroach
Cockroaches are insects of the order Blattaria or Blattodea, of which about 30 species out of 4,500 total are associated with human habitations...
es, locust AKH was inserted into a cockroach and a similar increase in lipid mobilisation was observed. Conversely, cockroach AKH led to similar activity within a locust.
AKH has become an important area of study, particularly in insect crop pests and insects that act as intermediate or vector hosts for parasites that can affect humans or agricultural animals. It is believed that AKH does not only aid flight in insects, but it has also been shown that an increase in AKH can lead to stronger immune responses in locusts . One group have performed experiments where locusts received an injection including AKH and lipopolysaccharide
Lipopolysaccharide
Lipopolysaccharides , also known as lipoglycans, are large molecules consisting of a lipid and a polysaccharide joined by a covalent bond; they are found in the outer membrane of Gram-negative bacteria, act as endotoxins and elicit strong immune responses in animals.-Functions:LPS is the major...
(LPS) – an immune elicitor found in the cell walls of bacteria – led to a stronger immune response than locusts which only received an LPS injection . This implies that lipid mobilisation by AKH can have a variety of uses for energy dynamics within insects and may be important in a range of functions that are related to insect survival. It is now believed that parasites which infect insects may stimulate the production of AKH in order to mobilise lipids which can then be used for parasite gains.