the wax moth Galleria melonella, 50 % of JH III
degradation in the fat body at the onset of the last
larval stage occurs via ester hydrolysis; in the
integument the value is 80 % and in the silk
glands it is 90 %. The involvement of epoxide
hydration increases during this larval stage.
Epoxide ether hydrolases (formerly epoxide
hydratases) have been found in numerous insects.
They are present in various tissues, especially in
the fat body and the midgut, but are not found in
the haemolymph [83,282]. Esterases with the
capacity to cleave juvenile hormones occur in the
haemolymph of probably all insects. However, a
distinction between specific JH esterases and specific "general" esterases is not easy to make so
long as none of them have been purified to homogeneity. The characteristics of such enzymes
appear to be that they show little activity with the
typical substrates of unspecific esterases, such as
a-naphthyl acetate ; that they cleave not only free
juvenile hormone but also that bound to specific
carrier proteins; and that they show little inhibition by diisopropylfluorophosphate (DP).
Attempts to purify JH esterases have so far been
mainly undertaken for the Lepidoptera. The
enzymes vary greatly in molecular mass between
34 and more than 100 kDa [53, 225, 269, 288].
The sequencing of a multiple JH esterase from
the moth Heliothis virescens showed the enzyme
to be a serine carboxyl esterase [86].
The haemolymph of many insects contains JHbinding proteins (JHBPs), which can be classified
as low affinity (KD ;?: 10- 5 moUI) or high affinity
(KD :5 1O- 7 moUI). Amongst the high-affinity
JHBPs are some with low (20-40 kDa) and some
with high (100-450 kDa) molecular masses. Low
molecular weight JHBPs are typical of the Lepidoptera, but also occur together with high molecular weight JHBPs in Chironomus thummi [283].
Blattodea, Orthoptera, Coleoptera and Diptera
all have exclusively high molecular weight JHBPs
[218, 237]. In the cockroaches Periplaneta americana and Leucophaea madeira, the beetle Leptinotarsa decemlineata and the non-biting midge
Chironomus thummi, but not in the locust
Locusta migratoria, the high molecular weight
JHBP is identical to the lipid shuttle protein lipophorin [136,218, 283]. The JHBPs immediately
take up the juvenile hormone released from the
corpora allata, prevent its transfer to lipid stores,
and thereby maintain its availability in the haemolymph. The high-affinity JHBPs protect the
juvenile hormone from degradation by unspecific
esterases, but because of their even higher affinities the specific JH esterases are able to remove
References
615
juvenile hormone from the carrier proteins and
hydrolyse it. Protection of the hormone from
esterolytic cleavage by JHBPs is thus only effective so long as the titre of the specific-JH esterases remains low, and the juvenile hormone concentration is regulated not only by biosynthesis
but mainly by the specific activity of JH esterases
[83].
The only JHBP to have been sequenced so far
is a monomer of 25 kDa (226 amino acids); this
was from the tobacco hornworm Manduca sexta.
Its sequence shows no similarity to any other protein and, consequently, constitutes a new protein
super-family [149]. The JHBPs are specific for the
juvenile hormone type. For example, the low
molecular weight JHBPs of Manduca sexta and
Galleria melonella bind the JH I and JH II, which
are typical of the Lepidoptera, much better than
the ubiquitous JH III; the reverse order is true
for the high molecular weight JHBPs from Leptino tarsus decemlineata, Chironomus thummi and
Drosophila melanogaster [200,237, 283]. The
JHBPs are also stereo-specific, e.g. the affinity of
the high molecular weight JHBP of the cockroach
Diploptera punctata is higher for the natural
10(R)-isomer of JH III than for the lO(S)-isomer
[131]. Intracellular JHBPs, which without doubt
also have receptor functions, have been reported
from various insects. In the epidermis of Manduca sexta, each cell nucleus contains about 10 4
molecules of a 29-kDa protein of high JH affinity,
and the cytoplasm has a 38-kDa protein with
lower affinity; this may be an intracellular JH carrier protein [202]. A JH III-specific, 85-kDa protein, isolated from the fat body of Drosophila
melanogaster, stimulates protein synthesis by
male accessory glands cultured in vitro, and is
apparently a JH receptor [238].
References
1. Abdel-Halim M. and Farah S. I.: Short time regulation
of acetyl CoA carboxylase. Compo Biochem. Physiol.
Pt. B 81: 9-19 (1985)
2. Aloia R. C. and Raison J. K.: Membrane function in
mammalian hibernation. Biochim. biophys. Acta 988:
123-146 (1989)
3. Araki S. et al.: Structure of a triphosphopentasoylceramide containing 4-0-methyl-N-acetylglucosamine from
the skin of the sea hare, Aplysia kurodai. J. bioI. Chern.
262: 14141-45 (1987)
4. Araki S. et al.: Novel phosphonoglycosphingolipids
containing pyruvylated galactose from the nervous system of Aplasia kurodai. Eur. J. Biochem. 198: 689-695
(1991)
degradation in the fat body at the onset of the last
larval stage occurs via ester hydrolysis; in the
integument the value is 80 % and in the silk
glands it is 90 %. The involvement of epoxide
hydration increases during this larval stage.
Epoxide ether hydrolases (formerly epoxide
hydratases) have been found in numerous insects.
They are present in various tissues, especially in
the fat body and the midgut, but are not found in
the haemolymph [83,282]. Esterases with the
capacity to cleave juvenile hormones occur in the
haemolymph of probably all insects. However, a
distinction between specific JH esterases and specific "general" esterases is not easy to make so
long as none of them have been purified to homogeneity. The characteristics of such enzymes
appear to be that they show little activity with the
typical substrates of unspecific esterases, such as
a-naphthyl acetate ; that they cleave not only free
juvenile hormone but also that bound to specific
carrier proteins; and that they show little inhibition by diisopropylfluorophosphate (DP).
Attempts to purify JH esterases have so far been
mainly undertaken for the Lepidoptera. The
enzymes vary greatly in molecular mass between
34 and more than 100 kDa [53, 225, 269, 288].
The sequencing of a multiple JH esterase from
the moth Heliothis virescens showed the enzyme
to be a serine carboxyl esterase [86].
The haemolymph of many insects contains JHbinding proteins (JHBPs), which can be classified
as low affinity (KD ;?: 10- 5 moUI) or high affinity
(KD :5 1O- 7 moUI). Amongst the high-affinity
JHBPs are some with low (20-40 kDa) and some
with high (100-450 kDa) molecular masses. Low
molecular weight JHBPs are typical of the Lepidoptera, but also occur together with high molecular weight JHBPs in Chironomus thummi [283].
Blattodea, Orthoptera, Coleoptera and Diptera
all have exclusively high molecular weight JHBPs
[218, 237]. In the cockroaches Periplaneta americana and Leucophaea madeira, the beetle Leptinotarsa decemlineata and the non-biting midge
Chironomus thummi, but not in the locust
Locusta migratoria, the high molecular weight
JHBP is identical to the lipid shuttle protein lipophorin [136,218, 283]. The JHBPs immediately
take up the juvenile hormone released from the
corpora allata, prevent its transfer to lipid stores,
and thereby maintain its availability in the haemolymph. The high-affinity JHBPs protect the
juvenile hormone from degradation by unspecific
esterases, but because of their even higher affinities the specific JH esterases are able to remove
References
615
juvenile hormone from the carrier proteins and
hydrolyse it. Protection of the hormone from
esterolytic cleavage by JHBPs is thus only effective so long as the titre of the specific-JH esterases remains low, and the juvenile hormone concentration is regulated not only by biosynthesis
but mainly by the specific activity of JH esterases
[83].
The only JHBP to have been sequenced so far
is a monomer of 25 kDa (226 amino acids); this
was from the tobacco hornworm Manduca sexta.
Its sequence shows no similarity to any other protein and, consequently, constitutes a new protein
super-family [149]. The JHBPs are specific for the
juvenile hormone type. For example, the low
molecular weight JHBPs of Manduca sexta and
Galleria melonella bind the JH I and JH II, which
are typical of the Lepidoptera, much better than
the ubiquitous JH III; the reverse order is true
for the high molecular weight JHBPs from Leptino tarsus decemlineata, Chironomus thummi and
Drosophila melanogaster [200,237, 283]. The
JHBPs are also stereo-specific, e.g. the affinity of
the high molecular weight JHBP of the cockroach
Diploptera punctata is higher for the natural
10(R)-isomer of JH III than for the lO(S)-isomer
[131]. Intracellular JHBPs, which without doubt
also have receptor functions, have been reported
from various insects. In the epidermis of Manduca sexta, each cell nucleus contains about 10 4
molecules of a 29-kDa protein of high JH affinity,
and the cytoplasm has a 38-kDa protein with
lower affinity; this may be an intracellular JH carrier protein [202]. A JH III-specific, 85-kDa protein, isolated from the fat body of Drosophila
melanogaster, stimulates protein synthesis by
male accessory glands cultured in vitro, and is
apparently a JH receptor [238].
References
1. Abdel-Halim M. and Farah S. I.: Short time regulation
of acetyl CoA carboxylase. Compo Biochem. Physiol.
Pt. B 81: 9-19 (1985)
2. Aloia R. C. and Raison J. K.: Membrane function in
mammalian hibernation. Biochim. biophys. Acta 988:
123-146 (1989)
3. Araki S. et al.: Structure of a triphosphopentasoylceramide containing 4-0-methyl-N-acetylglucosamine from
the skin of the sea hare, Aplysia kurodai. J. bioI. Chern.
262: 14141-45 (1987)
4. Araki S. et al.: Novel phosphonoglycosphingolipids
containing pyruvylated galactose from the nervous system of Aplasia kurodai. Eur. J. Biochem. 198: 689-695
(1991)