PK/MT controls the muscle contraction of the heart, gut,
and Malpighian tubules. This class of peptides was isolated
from the cerebral and abdominal neurohemal organs of many
insects. These peptides share the C-terminal FXPRL-NH2,
but their lengths and N-terminal sequences are variable.
Most PK/MT peptides share a common C-terminal
sequence, FXPRL-NH2. Therefore, these peptides are
classified as members of the FXPRLamide peptide family.
PK/MT is widely conserved among insects.
Gene, mRNA, and precursor
In D. melanogaster, the hugin gene encoding PK-2 and
hugγ peptides and the capa gene encoding MT-I (PK-1)
have been cloned. In the silkworm Bombyx mori, the capa
gene codes for CAPA-PK1, but its function is still
unclear.4–9 Unfortunately, the genes encoding the PK/
MTs of Leucophaea maderae and Locusta migratoria have
not yet been reported.
See Subchapters 75A and 75B for the distribution of
DH and PBAN receptors, respectively. Leucophaea
maderae PK shows moderate myostimulatory activity
on hindgut contraction and strong activity on foregut
and oviduct contraction.Locusta migratoria PK and MT
have a myostimulatory effect on cockroach hindgut contraction. On the other hand, hugγ is thought to function
as a molting control factor and to be involved in feeding
behavior.In Helicoverpa zea, this peptide family causes
melanization in larvae and pheromone production in
females and is designated as a pheromonotropic melanizing
peptide (Hez-PMP).
