1/16/12 Biological and chemical properties of the secretion from the hypobranchial gland of the purple snail … 1/17 www.highbeam.com/doc/1G1-135967942.html/print August 1, 2005 | Naegel, Ludwig C.A.; Alvarez, Jesus I. Murillo Biological and chemical properties of the secretion from the hypobranchial gland of the purple snail Plicopurpura pansa (Gould, 1853). ABSTRACT The hypobranchial gland of the muricid Plicopurpura pansa (Gould, 1853) is so active that the snails can be stimulated periodically without harming them to expulse the secretion. This property is a great advantage in the study about its biologic and chemical characteristics. No statistical difference could be determined between the incidence of expulsion and the sex of the animals. Also the test on whether the size of the animals had an influence on the frequency of expulsion showed no relation. The incidence of expulsions is the same between the different size classes. From between September 2003 and February 2005 collected snails (total number 3,577) 1,724 (48.2%) expulsed secretion. The proportion of snails that expulsed or not varied from month to month, however no clear seasonal trend could be observed. We determined in the laboratory the amount of the total organic compounds in the "milk" and found great variations (from 34.2 mg/100 animals to 337.8 mg/100 animals). We determined from 11 samples collected during different months an average of 148.9 mg organic compounds/100 animals. The "milk" expulsed from the hypobranchial gland of P. pansa contains 6.15% ([+ or -] 1.07 SD n = 3) total solids, 21.3 mg/ml ([+ or -] 17.8 SD n = 38) soluble proteins, and 6.01 mg/ml ([+ or -] 3;2 SD n = 38) carbohydrates. In organic extracts from the secretion of the hypobranchial gland we determined in a microwell assay a 50% lethal dose ([LD.sub.50]) of 81.72 [micro]g/mL (SD 35.78 n = 5) against Anemia nanplii. In assays to determine possible antibacterial activities in organic extracts we found two inhibition zones against Staphylococcus aureus. To quantify the microbial activity we determined a lowest inhibitory concentration of 125 [micro]g/disk. By thin layer- and column chromatography, as well as by IR spectroscopy, we could preliminary identify some of the organic compounds in the "milk" and in organic extracts. By comparing previously reported front reference values (Rf-values) we could identify the dye precursor tyrindolinone, tyriverdin and bromoisatin. By column chromatography the extract was separated with different mixtures of organic solvents. In a first step gradient fractionation we obtained three fractions, which were unstable in light and Journal of Shellfish Research
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1/16/12 Biological and chemical properties of the secretion from the hypobranchial gland of the purple snail …
1/17www.highbeam.com/doc/1G1-135967942.html/print
August 1, 2005 | Naegel, Ludwig C.A.; Alvarez, Jesus I. Murillo
Biological and chemical properties of thesecretion from the hypobranchial gland of thepurple snail Plicopurpura pansa (Gould, 1853).
ABSTRACT The hypobranchial gland of the muricid Plicopurpura pansa (Gould,
1853) is so active that the snails can be stimulated periodically without harming them
to expulse the secretion. This property is a great advantage in the study about its
biologic and chemical characteristics. No statistical difference could be determined
between the incidence of expulsion and the sex of the animals. Also the test on
whether the size of the animals had an influence on the frequency of expulsion
showed no relation. The incidence of expulsions is the same between the different size
classes. From between September 2003 and February 2005 collected snails (total
number 3,577) 1,724 (48.2%) expulsed secretion. The proportion of snails that
expulsed or not varied from month to month, however no clear seasonal trend could
be observed. We determined in the laboratory the amount of the total organic
compounds in the "milk" and found great variations (from 34.2 mg/100 animals to
337.8 mg/100 animals). We determined from 11 samples collected during different
months an average of 148.9 mg organic compounds/100 animals. The "milk"
expulsed from the hypobranchial gland of P. pansa contains 6.15% ([+ or -] 1.07 SD
n = 3) total solids, 21.3 mg/ml ([+ or -] 17.8 SD n = 38) soluble proteins, and 6.01
mg/ml ([+ or -] 3;2 SD n = 38) carbohydrates. In organic extracts from the secretion
of the hypobranchial gland we determined in a microwell assay a 50% lethal dose
([LD.sub.50]) of 81.72 [micro]g/mL (SD 35.78 n = 5) against Anemia nanplii. In
assays to determine possible antibacterial activities in organic extracts we found two
inhibition zones against Staphylococcus aureus. To quantify the microbial activity we
determined a lowest inhibitory concentration of 125 [micro]g/disk. By thin layer- and
column chromatography, as well as by IR spectroscopy, we could preliminary identify
some of the organic compounds in the "milk" and in organic extracts. By comparing
previously reported front reference values (Rf-values) we could identify the dye
precursor tyrindolinone, tyriverdin and bromoisatin. By column chromatography the
extract was separated with different mixtures of organic solvents. In a first step
gradient fractionation we obtained three fractions, which were unstable in light and
Journal of Shellfish Research
1/16/12 Biological and chemical properties of the secretion from the hypobranchial gland of the purple snail …
2/17www.highbeam.com/doc/1G1-135967942.html/print
turned immediately purple, and one yellow, light stable fraction. Two light stable
brownish-colored fractions turned purple after acid hydrolysis. They were united and
subjected to further fractionation, where four fractions and the green insoluble
tyriverdin were obtained. By IR spectrophotometry and comparison with reported
spectra it could be shown that one fractionated compound was a salt of probably 6-
bromo-2-methylsulfonylindoxylsulfate and the other 6-bromoisatin. In organic
extracts of the secretion free radical scavenging activities were determined by the 2,2-
dipbenyl-l-picrylhydrazyl radical method (DPPH). We observed two yellow patches
above a purple background. By IR spectroscopy of the organic extract used we could
determine the chromogen IV, probably 6-bromo-2 methylsulfonylindoxylsulfate, as a
substance responsible for the free radical scavenging activity.
KEY WORDS: purple snail, Plicopurpura pansa, hypobranchial gland, biological and
chemical properties
INTRODUCTION
The majority, if not all, of the marine snails from the family Muricidae produce in the
hypobranchial (mucous) gland a colorless secretion, which turns on exposure to air
and light to "Tyrian purple" (Fretter & Graham 1994).
In pre-Roman and Roman times "Tyrian purple" from the Mediterranean muricids
Murex trunculus, M. brandaris and Purpura haemastoma was a most expensive
luxury article, however with the Arab conquest of Palestine in 638 A.D. and finally
with the fall of Constantinople in 1453 A.D. the use of "Tyrian purple" became, with a
few exceptions, extinct in the Old World and the details about the dyeing methods
were forgotten.
For the scientific world it was therefore a big surprise when in 1685 William Cole
reported that the contents of the hypobranchial gland of the muricid Nucella lapillus
could directly be applied to linen and after a series of chemical reactions in the
presence of light and oxygen "Tyrian purple" is formed (Cole 1685). After his finding
numerous scientists tried to understand the chemical processes involved in the
production of "Tyrian purple". Bizio (cited in Ghiretti 1994) showed in 1835 that color
differences in the pigment from M. brandaris and M. trunculus are species-specific
and not related to ecology, as considered before, and that the dye had the chemical
properties of indigoid pigments. By processing the hypobranchial glands of 12,000 M.
brandaris snails Friedlander (1909) obtained 1.4 g of the pure pigment and by
elemental analysis he showed that the pigment contained bromine and that it was
6,6'-dibromoindigo. Syntheses confirmed his conclusion. Using advanced analytical
methods, Fouquet (1970), Baker and Duke (1973), Michel et al. (1992), Koren (1994),
Withnall et al. (2003) among others, have confirmed that the major pigment from
muricids is 6,6'-dibromoindigo, with dibromoindirubin and monobromoindigo as
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minor components. The exception is M. trunculus where the secretion contains both
brominated and nonbrominated dye precursors and because of cross coupling of
different indoxyl or indoleninone chromogens leading to a mixture of a high
concentration of 6-bromoindigo with indigo, indirubin and dibromoindigo (Wouters
1992, Koren 1994, Cooksey 2001). However, 6,6'-dibromoingigo and the other minor
indigoid pigments as such do not occur in the live animal, but are formed from
colorless dye precursors during a sequence of chemical reactions, requiring light,
oxygen and specific enzymes. First a yellow color is immediately formed, followed by a
greenish shade, and under the influence of oxygen and light changing to bluish,
which in turn changes finally into the purple dye, while liberating garlic-like smelling
volatile products, which have been determined by gas chromatography-mass
spectroscopy as methylmercaptan and dimethyl-disulfide (Shiomi et al. 1983).
After the development of new analytical methods the exact determination and
description of the different precursors leading to "Tyrian Purple" was only recently
possible. Cooksey (2001) described the different precursors and summarized the
entire process of the purple generation from excretions from the hypobranchial gland
from M. brandaris and M. trunculus.
The first steps in the chemical reactions towards purple are probably the degradation
of the essential amino acid tryptophan to indole and the hydroxylation into the
colorless indoxyl (Verhecken 1989). Indoxyl sulfate is formed through the sulfation of
indoxyl, which undergoes bio-bromination in the presence of hydrogen peroxide and
bromide by the membrane bound enzyme hromoperoxidase, leading to the colorless
tyrindoxyl sulfate.
Gribble (1998) described the reactions leading from the natural bromide to
organobromine compounds (bio-bromination) in marine organisms. Jannun and Coe
(1987) determined in homogenates of the hypohranchial gland of M. trunculus
bromoperoxidase for the probably peroxide-induced bromination reaction.
The required enzyme for the hydrolysis of the sulfate group in tyrindoxyl sulfate
leading to the yellow tyrindoxyl has been determined as the cytoplasmatic
arylsulfatase by histochemical (Erspamer 1946) and enzymatical methods (Erspamer
1946, Fouquet 1970). In the presence of oxygen the red tyrinindoleninone and the
yellow tyrindolinone are formed. Those indoxyls, which have substituents in the 2-
position, are oxidized to indoleninones that dimerise to give the green photolabile
tyriverdin. Photolysis of tyriverdin gives dibromoindigo, the main component of
Tyrian purple, and the odorous dimethyl disulfide (Cooksey 2001).
After the main chemical routes leading to Tyrian purple were described the question
about the biologic role of the hypobranchial secretions still remains open. Fretter and
Graham (1994) consider the main function of the hypobranchial gland to be a
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secretor of mucus for trapping and cementing particulate matter sucked into the
mantle cavity with the respiratory water current, prior to its expulsion. In the
hypobranchial gland the purple precursors and the enzymes that induce the
transformation of the precursors into pigments are kept separate so that no reaction
occurs. The final dye "Tyrian purple" as such does not occur in live animals.
The pharmacologic action by extracts of the hypohranchial gland was discovered by
Dubois (1909), and he described for the first time their toxic effects limiting the
movement and finally paralyzing actions on the central nerve system in both warm-
and cold-blooded animals. More recently toxins and narcotizing agents have been
described from the hypobranchial gland such as serotonin (5-hydroxytryptamine),
murexine (urocanylcholine), choline ester and biogenic amines (Erspamer 1946, 1952;
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