Specificity of L-Alanine Transport in the Spine Epithelium of Paracentrotus Lividus (Echinoidea)

Abstract

In many marine invertebrates the presence of an active transport system for the epithelial absorption of amino acids has been conclusively demonstrated (Stephens, 1968. 1972; West, de Burgh & Jeal, 1977). It has been observed by several authors that inhibition of uptake of a given amino acid can occur in the presence of other amino acids, in a manner analogous to that observed in vertebrate gut absorption systems. Some examples are the work of Chapman & Taylor (1969) on whole Nereis virens, Ferguson (1968) on the digestive glands of Echinaster spinulosus, Ferguson (1971) on whole asteroids, Bamford & Stewart (1973 a, b) on Arenicola marina gut, and Bamford & McCrea (1975) on the gill of Cerastoderma edule.

Biology of the Integument

“…A similar carrier, shared by a number of neutral amino acids, has been reported for the spine epithelium of the purple urchin Paracentrotus lividus (De Burgh et al 1977, De Burgh 1978. Mediated influx of L-alanine (K t = 0.08 mM, J max =0.027/n mol g-1 min-I) was significantly inhibited by other neutral amino acids including glycine and the L-enantiomorphs of leucine, methionine, proline, phenylalanine and serine.…”

“…Final substrate concentration ratios (tissue/final medium) in excess of unity have been reported following integumental amino acid influx in holothuroids, ophiuroids, echinoids and crinoids (Ahearn and Townsley 1975, Stephens and Virkar 1966, De Burgh 1978, West 1978). It has been noted in the previous section that when exposed to normal seawater concentrations or higher, animals are capable of net uptake of these molecules into the integument.…”

Biology of the Integument

“…A similar carrier, shared by a number of neutral amino acids, has been reported for the spine epithelium of the purple urchin Paracentrotus lividus (De Burgh et al 1977, De Burgh 1978. Mediated influx of L-alanine (K t = 0.08 mM, J max =0.027/n mol g-1 min-I) was significantly inhibited by other neutral amino acids including glycine and the L-enantiomorphs of leucine, methionine, proline, phenylalanine and serine.…”

“…Final substrate concentration ratios (tissue/final medium) in excess of unity have been reported following integumental amino acid influx in holothuroids, ophiuroids, echinoids and crinoids (Ahearn and Townsley 1975, Stephens and Virkar 1966, De Burgh 1978, West 1978). It has been noted in the previous section that when exposed to normal seawater concentrations or higher, animals are capable of net uptake of these molecules into the integument.…”

Nutrient Absorption in Invertebrates

“…Amino acid uptake in echinoderms is typically saturable and described by Michaelis-Menten kinetics (see Table 16.6). In general, a-neutral amino acids are transported by a pathway or set of pathways with a broad specificity for this structural class of amino acid (25,124); cationic and anionic amino acids do not share this pathway (124). Stephens et al (428) reported that, compared to uptake of neutral amino acids, integumental tissues from the sand dollar Dendraster excentricus accumulated aspartate and lysine slowly and glutamate not at all.…”

“…Ligation of the mouth and anus does not influence rates of accumulation into marine worms (91,152,422,448,456), indicating that uptake does not involve ingestion of seawater and subsequent transport by digestive epithelia. Reports of uptake into the isolated body wall of marine worms (96), isolated gill tissue of marine bivalves (58,507), and isolated spines (124,126) and test (428) of echinoderms further implicate the general integument as the site of uptake of dissolved nutrients. In addition, autoradiograms of animals exposed to exogenously applied, radiolabeled, organic molecules show that accumulated materials appear first in integumental tissues-for example, annelids (95), bivalves (329,515), brachiopods (286), echinoderms (143,148,154,325,328), and pogonophores (263,264,415).…”

“…The ability to discriminate between different structural classes of substrate is a hallmark of carrier‐mediated transport processes. Integumental amino acid uptake, for example, ordinarily involves multiple transporters, each with a degree of specificity for a separate class of these compounds—for example, bivalves (60, 434, 508), coelenterates (382), echinoderms (118, 124), nemerteans (369), polychaetes (402, 404, 448), and rhyncocoeleans (152). Specific carrier‐mediated pathways for sugars have also been found to be broadly distributed—for example, bivalves (58, 319), coelenterates (380), and polychaetes (19, 28).…”

Biology of the Integument

“…A similar carrier, shared by a number of neutral amino acids, has been reported for the spine epithelium of the purple urchin Paracentrotus lividus (De Burgh et al 1977, De Burgh 1978. Mediated influx of L-alanine (K t = 0.08 mM, J max =0.027/n mol g-1 min-I) was significantly inhibited by other neutral amino acids including glycine and the L-enantiomorphs of leucine, methionine, proline, phenylalanine and serine.…”

“…Final substrate concentration ratios (tissue/final medium) in excess of unity have been reported following integumental amino acid influx in holothuroids, ophiuroids, echinoids and crinoids (Ahearn and Townsley 1975, Stephens and Virkar 1966, De Burgh 1978, West 1978). It has been noted in the previous section that when exposed to normal seawater concentrations or higher, animals are capable of net uptake of these molecules into the integument.…”

Nutrient Absorption in Invertebrates

“…Amino acid uptake in echinoderms is typically saturable and described by Michaelis-Menten kinetics (see Table 16.6). In general, a-neutral amino acids are transported by a pathway or set of pathways with a broad specificity for this structural class of amino acid (25,124); cationic and anionic amino acids do not share this pathway (124). Stephens et al (428) reported that, compared to uptake of neutral amino acids, integumental tissues from the sand dollar Dendraster excentricus accumulated aspartate and lysine slowly and glutamate not at all.…”

“…Ligation of the mouth and anus does not influence rates of accumulation into marine worms (91,152,422,448,456), indicating that uptake does not involve ingestion of seawater and subsequent transport by digestive epithelia. Reports of uptake into the isolated body wall of marine worms (96), isolated gill tissue of marine bivalves (58,507), and isolated spines (124,126) and test (428) of echinoderms further implicate the general integument as the site of uptake of dissolved nutrients. In addition, autoradiograms of animals exposed to exogenously applied, radiolabeled, organic molecules show that accumulated materials appear first in integumental tissues-for example, annelids (95), bivalves (329,515), brachiopods (286), echinoderms (143,148,154,325,328), and pogonophores (263,264,415).…”

“…The ability to discriminate between different structural classes of substrate is a hallmark of carrier‐mediated transport processes. Integumental amino acid uptake, for example, ordinarily involves multiple transporters, each with a degree of specificity for a separate class of these compounds—for example, bivalves (60, 434, 508), coelenterates (382), echinoderms (118, 124), nemerteans (369), polychaetes (402, 404, 448), and rhyncocoeleans (152). Specific carrier‐mediated pathways for sugars have also been found to be broadly distributed—for example, bivalves (58, 319), coelenterates (380), and polychaetes (19, 28).…”

Biology of the Integument

“…A similar carrier, shared by a number of neutral amino acids, has been reported for the spine epithelium of the purple urchin Paracentrotus lividus (De Burgh et al 1977, De Burgh 1978. Mediated influx of L-alanine (K t = 0.08 mM, J max =0.027/n mol g-1 min-I) was significantly inhibited by other neutral amino acids including glycine and the L-enantiomorphs of leucine, methionine, proline, phenylalanine and serine.…”

“…Final substrate concentration ratios (tissue/final medium) in excess of unity have been reported following integumental amino acid influx in holothuroids, ophiuroids, echinoids and crinoids (Ahearn and Townsley 1975, Stephens and Virkar 1966, De Burgh 1978, West 1978). It has been noted in the previous section that when exposed to normal seawater concentrations or higher, animals are capable of net uptake of these molecules into the integument.…”

Nutrient Absorption in Invertebrates

“…Amino acid uptake in echinoderms is typically saturable and described by Michaelis-Menten kinetics (see Table 16.6). In general, a-neutral amino acids are transported by a pathway or set of pathways with a broad specificity for this structural class of amino acid (25,124); cationic and anionic amino acids do not share this pathway (124). Stephens et al (428) reported that, compared to uptake of neutral amino acids, integumental tissues from the sand dollar Dendraster excentricus accumulated aspartate and lysine slowly and glutamate not at all.…”

“…Ligation of the mouth and anus does not influence rates of accumulation into marine worms (91,152,422,448,456), indicating that uptake does not involve ingestion of seawater and subsequent transport by digestive epithelia. Reports of uptake into the isolated body wall of marine worms (96), isolated gill tissue of marine bivalves (58,507), and isolated spines (124,126) and test (428) of echinoderms further implicate the general integument as the site of uptake of dissolved nutrients. In addition, autoradiograms of animals exposed to exogenously applied, radiolabeled, organic molecules show that accumulated materials appear first in integumental tissues-for example, annelids (95), bivalves (329,515), brachiopods (286), echinoderms (143,148,154,325,328), and pogonophores (263,264,415).…”

“…The ability to discriminate between different structural classes of substrate is a hallmark of carrier‐mediated transport processes. Integumental amino acid uptake, for example, ordinarily involves multiple transporters, each with a degree of specificity for a separate class of these compounds—for example, bivalves (60, 434, 508), coelenterates (382), echinoderms (118, 124), nemerteans (369), polychaetes (402, 404, 448), and rhyncocoeleans (152). Specific carrier‐mediated pathways for sugars have also been found to be broadly distributed—for example, bivalves (58, 319), coelenterates (380), and polychaetes (19, 28).…”