Oyster Protein Research Articles

Pharmacological characterization of serotonin receptor in the oocyte membrane of bivalve molluscs and its formation during oogenesis

Serotonin (5-hydroxytryptamine, 5-HT) is a major neurotransmitter that triggers the spawning of bivalve molluscs and oocyte germinal vesicle breakdown (GVBD) of oocytes. The present study employed [3H] 5-HT binding assay to characterize a putative receptor on oocyte membranes prepared from scallops and oysters. Results demonstrated a profile of hormone control of 5-HT receptor formation during oocyte growth. The dissociation constants for 5-HT on the surfaces of scallop and oyster oocytes were estimated to be 2.64 μM and 2.01 μM, respectively, and the maximal binding capacity of the oocyte surface was 152 pmol/mg protein in scallops and 529 pmol/mg protein in oysters. The inhibition of [3H] 5-HT bound by various agonists and antagonists provided pharmacological evidence for a 5-HT receptor in each oocyte, a mixed profile of 5-HT1/5-HT2 in scallops and a single profile of 5-HT1 in oyster. Formation of 5-HT receptor on the surface of the scallop oocyte was induced by estradiol-17β(E2), which was suggested as a primary promoter of the effect of E2 on sensitivity to 5-HT, resulting in the induction of spawning. This formation occurred during oocyte growth controlled by E2. J. Exp. Zool. 281:124–131, 1998. © 1998 Wiley-Liss, Inc.

Behavior of metallothionein-bound metals in a natural population of an estuarine mollusc

A population of oysters ( Crassostrea virginica) in the estuarine reaches of the Patuxent River (Maryland, USA) possesses elevated concentrations of certain metals and is known to exhibit a gradient in metal concentrations, increasing upstream from the mouth of the river. The accumulation of total Cd, Zn and Cu in the gill tissues of these oysters was analyzed and compared to the concentrations in the cytosol and bound to metallothioneins (MTs). The concentrations of the metals in the gill tissues exhibited the expected gradient, with concentrations increasing upstream. The acetylated form of oyster MT, CvNAcMT, was the main form of MT detected in these oysters. This is the expected form of this protein in oysters based on basic biochemical criteria and data obtained for oysters exposed to low concentrations of Cd in this study. MTs were quantitatively most significant in binding Cd, sequestering about 20% of the tissue Cd, and much less so in binding Zn and Cu, accounting for about 0·3 and 1·0%, respectively, of these metals. Complex relationships were observed when the cytosolic and MT-bound fractions of these metals were compared with the total metal concentrations. Of greatest interest was the observation that concentrations of the MT-bound fractions declined in oysters collected from the site with the highest tissue metal concentrations. Zinc bound to MTs did not exhibit any correlation with either the total or cytosolic metal concentrations. With Cd and Cu, however, strong relationships were observed between MT-bound and cytosolic fractions, irrespective of the total tissue metal concentrations. With these metals, the relative distribution on MT-bound fractions could be predicted from the cytosolic concentrations, but not from the total tissue metal concentration. The amounts of Cd bound to MTs was inversely related to that of Zn. Cu was usually bound at low concentrations, except in a few individuals whose MTs were Zn-rich and Cu-rich. The relatively complex nature of the dynamics of MT-bound metals indicated that increased emphasis should be placed on determining the sources of variability in the utilization of MTs in binding metals in these molluscs.

Sequence and atomic-force microscopy analysis of a matrix protein from the shell of the oyster Crassostrea virginica

Atomic-force microscopy of the major class of soluble matrix protein from the oyster Crassostrea virginica revealed that this protein forms a ring structure, perhaps rendering the NH2-terminus unavailable to Edman degradation. Cleavage of these proteins using mild acid hydrolysis and hydroxylamine produced linear peptides that were able to be sequenced. Peptides consisted of a domain of polyserine-phosphoserine and runs of aspartic acid of 4 to 7 residues, with several other amino acids present. Hydrophobic domains were also isolated. Although phylogenetically distant, oyster shell-matrix protein is similar to the phosphophoryn isolated from dentin and, to a lesser extent, proteins isolated from verteorate bone.

アコヤガイタンパク質の栄養価に関する研究

The amino acids composition and nutritive values of pearl oyster proteins were examined. The amino acid score of pearl oyster proteins was 88. Growth rates of rats fed a pearl oyster diet were higher than those fed a casein diet. True digestibility of pearl oyster proteins was lower than that of casein. The nutritive values of pearl oyster proteins measured for rats were about the same as those of casein. The level of total plasma cholesterol in rats fed the pearl oyster diet was lower than that of those fed the casein diet. Pearl oyster was thus considered to be a useful protein source, which could control the accumulation of total plasma cholesterol.

Effect of environmental factors and parasitism on hemolymph lysozyme and protein of American oysters ( Crassostrea virginica)

The biological roles of lysozymes in bivalves are believed to be involved with the mechanisms of host defense and digestion. Experiments were carried out to examine hemolymph lysozyme activity and protein in oysters over a 1-year period to determine their relationship with seasonal environmental variables (temperature, salinity, and food availability) and whether they correlate with parasitism by Perkinsus marinus. Hemolymph lysozyme and protein exhibited seasonal fluctuations. Hemolymph lysozyme varied greatly between individual oysters, and it was higher in winter months than in summer months. No linkage was found between hemolymph lysozyme and protein concentration and infection of oysters by P. marinus. It is argued that the observed seasonal changes in hemolymph lysozyme and protein may relate to the oyster reproductive cycle.

Characterization Studies on the Cadmium-Binding Proteins from Two Species of New Zealand Oysters

Two different types of New Zealand oysters--Ostrea lutaria (OL) and Crassostrea glomerata (CG)--contained different concentrations of zinc, copper, and cadmium. OL oysters had 5.3 micrograms Cd/g, 3.4 micrograms Cu/g, 100 micrograms Zn/g; CG oysters had 1.4 micrograms Cd/g and 936 micrograms Zn/g. Both kinds of oysters were shown by gel filtration (G-75) to contain cadmium and zinc in fractions corresponding to a high molecular weight protein (corresponding to the size of albumin or larger) which was heat labile. OL oysters contained cadmium in fractions corresponding to a molecular weight of approximately 6500. The cadmium-binding protein in these fractions was heat-stable. This protein contained no detectable amounts of zinc and was not present in the CG oysters. Further purification by gel filtration (G-50) was performed to obtain a purer protein fraction. Isoelectric focusing of the protein obtained by G-50 filtration showed one main fraction of protein with a pI approximately 5.9 at approximately 13 degrees C. CG oysters contained cadmium and zinc in a polypeptide with low molecular weight (MW 1000). The cadmium-binding oyster proteins are minimally reactive in a competitive binding radioimmunoassay in comparison to the reactivity of a typical vertebrate metallothionein; the proteins may be metallothioneins, but, if so, they do not exhibit the principal determinants characteristic of vertebrate metallothioneins.

Characterization studies on the cadmium-binding proteins from two species of New Zealand oysters.

Two different types of New Zealand oysters--Ostrea lutaria (OL) and Crassostrea glomerata (CG)--contained different concentrations of zinc, copper, and cadmium. OL oysters had 5.3 micrograms Cd/g, 3.4 micrograms Cu/g, 100 micrograms Zn/g; CG oysters had 1.4 micrograms Cd/g and 936 micrograms Zn/g. Both kinds of oysters were shown by gel filtration (G-75) to contain cadmium and zinc in fractions corresponding to a high molecular weight protein (corresponding to the size of albumin or larger) which was heat labile. OL oysters contained cadmium in fractions corresponding to a molecular weight of approximately 6500. The cadmium-binding protein in these fractions was heat-stable. This protein contained no detectable amounts of zinc and was not present in the CG oysters. Further purification by gel filtration (G-50) was performed to obtain a purer protein fraction. Isoelectric focusing of the protein obtained by G-50 filtration showed one main fraction of protein with a pI approximately 5.9 at approximately 13 degrees C. CG oysters contained cadmium and zinc in a polypeptide with low molecular weight (MW 1000). The cadmium-binding oyster proteins are minimally reactive in a competitive binding radioimmunoassay in comparison to the reactivity of a typical vertebrate metallothionein; the proteins may be metallothioneins, but, if so, they do not exhibit the principal determinants characteristic of vertebrate metallothioneins.

Seasonal and environmental variation in protein and carbohydrate levels in the hemolymph from American oysters ( Crassostrea virginica gmelin)

1. 1. Carbohydrate and protein levels in cell-free hemolymph of Crassostrea virginica exhibited a pronounced seasonal cycle, possibly linked to the oyster's reproductive cycle. 2. 2. There were persistent differences in the hemolymph carbohydrate and protein levels between oysters collected from different localities. 3. 3. The influence of laboratory changes in temperature and salinity, alone and in combination, on the oyster's hemolymph carbohydrate and protein concentration varied according to the season and site of collection. 4. 4. Hemolymph protein and carbohydrate levels in oysters starved for 7 days did not differ from those in fed animals.

Influence of adsorption time, rocking, and soluble proteins on the plaque assay of monodispersed poliovirus.

Factors that could affect adsorption of monodispersed poliovirus to cell culture monolayers were evaluated. These included varying the virus adsorption period under static and nonstatic (rocked) conditions and altering the rocking rate. The effects of several soluble proteins on plaque formation, enumeration, and size were also evaluated. Rocking involved the mechanical spread of viruses over cell culture monolayers for 1 to 4 h. Rocked cultures exhibited significantly higher (P less than 0.05) plaque counts than corresponding static cultures. Optimal plaque counts were obtained after a 2-h adsorption period with rocking; increasing the period to 4 h did not significantly increase PFU. Optimal counts were not obtained until greater than or equal to 4 h with static adsorption. Plaque counts were not affected by increasing the rocking rate above one oscillation per minute, but a slower rocking rate resulted in a significant decrease in plaques. Adsorption of poliovirus in the presence of 3% solutions of beef and meat extracts, acid-precipitated oyster protein, two brands of skim milk, and 3 and 10% fetal bovine serum was compared with adsorption in protein-free controls. Significant reductions (P less than 0.05) in plaque counts occurred with one brand of skim milk, whereas 3% beef extract yielded highly significant reductions (P less than 0.01) in plaque counts and appreciable decreases in plaque sizes. Salinities of protein-containing virus inocula were high for beef and meat extracts but somewhat below physiological levels for the remaining inocula. Beef extract-associated reductions in PFU were eliminated after the extracts were dialyzed. Plaque reductions were associated with dialyzable components of the beef extract but not with the inoculum salinity.

The nature of cadmium binding in commercial eastern oysters (Crassostrea virginica).

In contrast to previous results which examined oysters exposed to artificially high cadmium (Cd) levels, the forms of cadmium occurring in “natural” commercially available oysters were partially characterized. About one-third of the Cd was associated with insoluble material. Of the soluble Cd, about 20% occurred in a high molecular weight protein of 40,000–50,000 daltons. The low molecular weight soluble Cd consisted of at least two different forms,i.e., that associated with amino acids (a small peptide) and inorganic Cd. The small peptide fraction also contained zinc and copper. The forms of Cd in commercial oysters were compared to those occurring in both commercial scallops and artificially cultured oysters. Scallops bind Cd to three soluble proteins, all of which are of higher molecular weight than the small oyster peptide. Oysters cultured in 10 ppb Cd medium contained binding sites similar to commercial oysters except that none of the soluble Cd in the cultured oysters was associated with a high molecular weight protein. The results suggest that extremely high environmental Cd levels are necessary to induce a metallothionein-like protein in oysters. Implications of the results to public health are discussed.

Rapid methods for extraction and concentration of poliovirus from oyster tissues

A procedure is discussed for the extraction of poliovirus from oyster meats by modification of several enterovirus extraction techniques. The modified method uses meat extract and Cat-Floc, a polycationic electrolyte, for virus extraction and concentration. Virus recovery from inoculated oyster homogenates is 93–120%. Adsorption of viruses to oyster proteins by acidification of homogenates does not affect virus recovery. Elution of viruses from oyster proteins appears more efficient at pH 9.5 than at pH 8.0. This technique is relatively simple, economical and requires only 2.5 h to complete the combined extraction and concentration procedure.

Factors influencing cadmium accumulation and its toxicity to marine organisms.

The toxicity of dissolved cadmium to a variety of marine animals has been found to be related to salinity, with decreased toxicity observed at higher salinities. Recent data from our laboratory have demonstrated that the toxicity of cadmium to estuarine shrimp and larval fish is a function of free cadmium ion concentration, which in turn is controlled by the chloride concentration of the water. As the chloride concentration (i.e., salinity of the water) increases, the concentration of free cadmium ion decreases relative to total dissolved metal, due to its complexation with chloride ions. These observations have been given further support by measurements involving the uptake of (115m)Cd by shrimp which showed that accumulation of (115m)Cd and chloride concentration also are inversely related. Experiments also have been conducted on the physiological effects of cadmium on the respiration of excised oyster gill tissue. Although tissues from oysters exposed for 14 days to 0.1 ppm total dissolved cadmium accumulated significant quantities of metal, no measurable effects on respiration rates were detected. Higher doses (0.3 and 0.6 ppm) caused both mortalities of oysters and accelerated respiration of excised oyster gill. Exposure to 0.1 ppm cadmium also caused the induction of and/or increased binding of cadmium to a specific low molecular weight protein in oysters. This protein appeared to have a detoxification function at low cadmium exposure levels, but in animals exposed to 0.6 ppm cadmium the induction mechanism apparently became saturated, allowing the excess cadmium to bind critical sites with resultant damage.

Factors Influencing Cadmium Accumulation and Its Toxicity to Marine Organisms

The toxicity of dissolved cadmium to a variety of marine animals has been found to be related to salinity, with decreased toxicity observed at higher salinities. Recent data from our laboratory have demonstrated that the toxicity of cadmium to estuarine shrimp and larval fish is a function of free cadmium ion concentration, which in turn is controlled by the chloride concentration of the water. As the chloride concentration (i.e., salinity of the water) increases, the concentration of free cadmium ion decreases relative to total dissolved metal, due to its complexation with chloride ions. These observations have been given further support by measurements involving the uptake of 115mCd by shrimp which showed that accumulation of 115mCd and chloride concentration also are inversely related. Experiments also have been conducted on the physiological effects of cadmium on the respiration of excised oyster gill tissue. Although tissues from oysters exposed for 14 days to 0.1 ppm total dissolved cadmium accumulated significant quantities of metal, no measurable effects on respiration rates were detected. Higher doses (0.3 and 0.6 ppm) caused both mortalities of oysters and accelerated respiration of excised oyster gill. Exposure to 0.1 ppm cadmium also caused the induction of and/or increased binding of cadmium to a specific low molecular weight protein in oysters. This protein appeared to have a detoxification function at low cadmium exposure levels, but in animals exposed to 0.6 ppm cadmium the induction mechanism apparently became saturated, allowing the excess cadmium to bind critical sites with resultant damage.

仕立て作業および挿核手術がアコヤガイの生理状態に及ぼす影響

In the pearl culture “Shitate-sagyo” is regarded as a necessary process prior to the operation of nuclear insertion. The objective of this process is generally accepted to make oysters spawn so as to produce conditions of gonad suitable for the operation. The method is as follows; the oysters are placed densely in bamboo-cages, and are laid over the bottom or suspended again from rafts for an artificial spawnning, during the period of not loss than two weeks. In previous studies1), however, the author calarified that Shitate-sagyo checks physiological decline and mortality of oysters and fall of inserted nuclei after the operation, and thus brings good results in the yield and quality of pearls. In view of accumulating further information concerning the physiological effects of Shitate-sagyo on oysters investigation was made on changes in both protein and carbohydrate metabolism in oysters which underwent Shitate-sagyo. In an attempt to estimate the balance between anabolism and catabolism in the protein metabolism, amount of serum protein and that of rest-N were measured. Measurement was also made of weight of crystallins style and amount of lactic acid in serum in relation to the carbohydrate metabolism. Measurements revealed that Shitate-sagyo brought oysters decreases in both anabolism and catabolism in either of the protein and carbohydrate metabolism (Fig. 2, 4, 6). This means that oysters were physiologically reperssed by Shitate-sagyo. When oysters first went through Shitate-sagyo and then received the operation catabolism as well as anabolism was intensified in both metabolism to some extent. As a result the balance between them was maintained (Fig. 7, 8). On the contrary in case of oysters which underwent no Shitate-sagyo catabolism in both metabolism were intensified to a large extent after the operation, while anabolism were reduced, that is the balance was disturbed. From the above it is concluded that a physiological repression caused in oysters by Shitate-sagyo provides a condition necessary for the maintenance of balance in their meta-bolism after the operation.