e.g. fast atom bombardment spectroscopy and
the new possibilities for cDNA and gene sequencing, has led, during the last few years to rapid
increases in the number of available sequences
[104, 115, 166, 219]. The invertebrate peptide
hormones are also produced from larger precursors by proteolytic processing and, in many cases,
are also post-translationally modified. The formation of D-amino acid residues from the L-forms of
the precursors, as described above for the dermorphins of the vertebrates, has also been
described for the mollusc peptides, achatin and
fulicin [104, 158]. The discovery of a new peptide
hormone in anyone animal group is often followed by evidence that this or similar substances
occur in other groups, or are even ubiquitous.
Examples of this are provided by the detection of
vertebrate hormones in invertebrates or the discovery of peptides similar to the mollusc FMRFamide in cnidarians, annelids and insects [104].
Comparisions across taxon borders should allow a
deeper insight into the relationships between
peptide structure and function. However, the
evolutionary relationships between the peptide
hormones cannot be determined from short
sequence comparisons because of the possibilities
of convergence. A much better basis for comparison are gene or precursor sequences but these
are, as yet, in short supply.
Apart from mollusc and arthropod hormones,
only a few regulatory peptides are known from
other invertebrate groups. Amongst these are the
sperm-activating peptides (SAPs) of sea urchin
eggs; these stimulate sperm metabolism and
motility and act as chemo-attractants for the spermatozoa. SAPs are peptides of 10-14 amino acids
which are species specific but occur in several
variant forms within one species. Forty different
SAPs have so far been described from nine sea
urchin species. The first of these substances
to be found were speract (GFDLNGGGVG)
from Strongylocentrotus purpuratus and resact
(CVTGAPGCVGGGRL-amide) from Arbacia
punctulata. Speract arises from a precursor of
about 260 amino acids containing 10 speract or
speract-like sequences [177,246]. The conjugation initiating substances of the ciliates have also
been intensively investigated. These unicellular
organisms proliferate asexually by fission; occasionally, a sexual process ( conjugation) occurs in
which two individuals fuse, exchange genetic
material, and separate. In some species, conjugation is restricted to individuals of opposite "mating types". Each mating type produces a different
conjugation initiating substance, and these are
8.8.1 Peptide Hormones of Molluscs
305
known generally as mating pheromones or gamones but are sometimes named after the genus.
Two gamones are known from Blepharisma japonicum, the first species to be investigated: blepharom, a basic glycoprotein of 20 kDa, and blepharisom, which has been identified as calcium3-(2'-formylamino-5'-hydroxybenzoyl)acetate. Genetic analysis of several species of the genus
Euplotes has shown that the gamones are
encoded by alleles of one gene locus. The pheromones Er-l (40 amino acids) and Er-l0 (38 amino
acids) of E. raikovi have been sequenced; they
show no similarity to any other proteins [175].
8.8.1 Peptide Hormones of Molluscs
It was known for some time that ganglion extracts
of various molluscs could amplify the contraction
of isolated hearts of the Venus mussel; the
responsible factor was later isolated from the
ganglia of the mussel Macrocallista nimbrosa and
was shown to be a C-terminal amidated tetrapeptide, FMRF-amide. This peptide is apparently
distributed ubiquitously in molluscs, mostly in
association with smaller amounts of the related
peptide FLRF-amide. The precursor of these
peptides from Aplysia californica has been
sequenced; it consists of 28 copies of the FMRF
sequence and only 1 FLRF sequence. Various
mollusc species have been found to possess variants of these two peptides with 1- to 6-amino-acid
N-terminal extensions (Fig.8.6a). The mussel
Mytilus produces a decapeptide which ends with
the FFRF-amide sequence. Whilst the peptides
mentioned so far all have stimulatory effects on
muscle contraction, a hexapeptide with the Cterminal sequence LFRF-amide, found in Fusinus, has an inhibitory effect. FMRF-amiderelated peptides (FaRPs), ending with FXRFamide, have been found in nematodes, annelids
and arthropods in addition to the molluscs, and
RF-amide-terminating peptides are even more
widely distributed. The evolutionary relationships
between these regulatory peptides will become
clear only after analysis of their gene or precursor
sequences has been undertaken [104]. A gene
sequenced from Drosophila melanogaster codes
for a polyprotein with at least 13 FaRP sequences,
and a cDNA from the sea anemone contains
19 precursor sequences of the antho-RF-amide
(QGRF-amide) [47, 193].
A large number of other myotropic peptides
and peptide amides have been found in the molluscs, e.g. the catch-relaxing peptide (CARP) of
the new possibilities for cDNA and gene sequencing, has led, during the last few years to rapid
increases in the number of available sequences
[104, 115, 166, 219]. The invertebrate peptide
hormones are also produced from larger precursors by proteolytic processing and, in many cases,
are also post-translationally modified. The formation of D-amino acid residues from the L-forms of
the precursors, as described above for the dermorphins of the vertebrates, has also been
described for the mollusc peptides, achatin and
fulicin [104, 158]. The discovery of a new peptide
hormone in anyone animal group is often followed by evidence that this or similar substances
occur in other groups, or are even ubiquitous.
Examples of this are provided by the detection of
vertebrate hormones in invertebrates or the discovery of peptides similar to the mollusc FMRFamide in cnidarians, annelids and insects [104].
Comparisions across taxon borders should allow a
deeper insight into the relationships between
peptide structure and function. However, the
evolutionary relationships between the peptide
hormones cannot be determined from short
sequence comparisons because of the possibilities
of convergence. A much better basis for comparison are gene or precursor sequences but these
are, as yet, in short supply.
Apart from mollusc and arthropod hormones,
only a few regulatory peptides are known from
other invertebrate groups. Amongst these are the
sperm-activating peptides (SAPs) of sea urchin
eggs; these stimulate sperm metabolism and
motility and act as chemo-attractants for the spermatozoa. SAPs are peptides of 10-14 amino acids
which are species specific but occur in several
variant forms within one species. Forty different
SAPs have so far been described from nine sea
urchin species. The first of these substances
to be found were speract (GFDLNGGGVG)
from Strongylocentrotus purpuratus and resact
(CVTGAPGCVGGGRL-amide) from Arbacia
punctulata. Speract arises from a precursor of
about 260 amino acids containing 10 speract or
speract-like sequences [177,246]. The conjugation initiating substances of the ciliates have also
been intensively investigated. These unicellular
organisms proliferate asexually by fission; occasionally, a sexual process ( conjugation) occurs in
which two individuals fuse, exchange genetic
material, and separate. In some species, conjugation is restricted to individuals of opposite "mating types". Each mating type produces a different
conjugation initiating substance, and these are
8.8.1 Peptide Hormones of Molluscs
305
known generally as mating pheromones or gamones but are sometimes named after the genus.
Two gamones are known from Blepharisma japonicum, the first species to be investigated: blepharom, a basic glycoprotein of 20 kDa, and blepharisom, which has been identified as calcium3-(2'-formylamino-5'-hydroxybenzoyl)acetate. Genetic analysis of several species of the genus
Euplotes has shown that the gamones are
encoded by alleles of one gene locus. The pheromones Er-l (40 amino acids) and Er-l0 (38 amino
acids) of E. raikovi have been sequenced; they
show no similarity to any other proteins [175].
8.8.1 Peptide Hormones of Molluscs
It was known for some time that ganglion extracts
of various molluscs could amplify the contraction
of isolated hearts of the Venus mussel; the
responsible factor was later isolated from the
ganglia of the mussel Macrocallista nimbrosa and
was shown to be a C-terminal amidated tetrapeptide, FMRF-amide. This peptide is apparently
distributed ubiquitously in molluscs, mostly in
association with smaller amounts of the related
peptide FLRF-amide. The precursor of these
peptides from Aplysia californica has been
sequenced; it consists of 28 copies of the FMRF
sequence and only 1 FLRF sequence. Various
mollusc species have been found to possess variants of these two peptides with 1- to 6-amino-acid
N-terminal extensions (Fig.8.6a). The mussel
Mytilus produces a decapeptide which ends with
the FFRF-amide sequence. Whilst the peptides
mentioned so far all have stimulatory effects on
muscle contraction, a hexapeptide with the Cterminal sequence LFRF-amide, found in Fusinus, has an inhibitory effect. FMRF-amiderelated peptides (FaRPs), ending with FXRFamide, have been found in nematodes, annelids
and arthropods in addition to the molluscs, and
RF-amide-terminating peptides are even more
widely distributed. The evolutionary relationships
between these regulatory peptides will become
clear only after analysis of their gene or precursor
sequences has been undertaken [104]. A gene
sequenced from Drosophila melanogaster codes
for a polyprotein with at least 13 FaRP sequences,
and a cDNA from the sea anemone contains
19 precursor sequences of the antho-RF-amide
(QGRF-amide) [47, 193].
A large number of other myotropic peptides
and peptide amides have been found in the molluscs, e.g. the catch-relaxing peptide (CARP) of