Adipokinetic hormone (AKH) is an insect neuropeptide produced by the corpora cardiaca, a neuroendocrine organ closely
associated with the insect brain. During high physical activities such as flight and intense locomotion, AKH is released into the circulation and transported to the fat body, where it binds to its G protein-coupled receptors (GPCRs). Activation of these GPCRs stimulates the release of carbohydrates (trehalose) and lipids, which are needed to fuel the high physical activity of the insect.
AKHs and their GPCRs, however, are also involved in hemolymph carbohydrate homeostasis by releasing trehalose under nonstress conditions, a process that in Drosophila larvae is counteracted by insulin-like peptides and the insulin receptor, which decrease hemolymph trehalose concentrations. Thus, AKH and insulin in insects act comparably to glucagon and insulin in mammals during blood sugar homeostasis.
The AKHs are a large family of small, structurally related peptides, all being 8 –10 amino acid residues long. AKHs occur in all insects investigated so far, with some insects producing more than one AKH. AKH peptides also occur in crustaceans, where they are named red pigment-concentrating hormone, because of their function in color adaptation. The insect corazonins are widespread in insects and are undecapeptides that are structurally related to the AKHs. The insect corazonin receptors have recently been identified. They do not cross-react with AKHs and the AKH receptors do not cross-react with corazonins, showing that these are two independent hormonal systems. Phylogenetic tree analyses show that not only the AKH and corazonin neuropeptides but also the AKH and corazonin receptors are closely related, suggesting co-evolution of receptors and ligands in a process, where the ancestor receptor and neuropeptide genes have duplicated. This is followed by mutations and evolutionary selection, leading to two independent hormonal systems each with its own physiological role.
Table 1 shows the sequence and theoretical molecular weight of some akh peptides that reported by researchers.
|Neuropeptide Name||Sequence||length(aa)||Chemical Formula||Mw average(g/mol)|
|Aplysia californica AKH||pEIHFSPDWGT-NH2||10||C55H72N14O15||1169.24|
|Lottia gigantea AKH||pEIHFSPTWGS-NH2||10||C54H72N14O14||1141.23|
|Bithynia siamensis goniomphalos AKH||pEIHFTPGWGS-NH2||10||C53H70N14O13||1111.2|
|Mytilus galloprovincialis AKH||pEISFSTDWGS-NH2||10||C50H68N12O17||1109.14|
|Hyriopsis cumingii AKH||pEISFSTNWGS-NH2||10||C50H69N13O16||1108.15|
|Locusta migratoria AKH-1||pELNFTPNWGT-NH2||10||C54H74N14O15||1159.24|
|Hypsibius dujardini AKH||pELSFSTGWGH-NH2||10||C51H68N14O14||1101.17|
|Globodera rostochiensis AKH||pEMTFSDGW-NH2||8||C43H56N10O13S||953.02|
|Crassostrea gigas AKH||pEVSFSTNWGS-NH2||10||C49H67N13O16||1094.13|
pE = Pyroglutamic acid
Souce: NovoPro 2018-06-25