W. Zurburg

Seasonal variations in biochemical composition of mytilus edulis with reference to energy metabolism and gametogenesis

Abstract 1. 1. Seasonal changes in biochemical composition in relation to energy metabolism and to gametogenesis were studied in Mytilus edulis for nearly one and a half year. 2. 2. During the whole experimental period animals were selected from samples of the same musselbed in the Dutch Wadden Sea at intervals of about three weeks. 3. 3. The biochemical composition of total tissues and different organs was analyzed. In growing mussels a gradual increase of protein, glycogen and lipid contents was observed from spring to autumn. From November to next April the protein and glycogen content declined, whereas the lipid content remained rather constant until spawning. The observed changes are discussed in relation to environmental parameters as temperature, salinity and nutrient levels, as well as to energy production and gametogenesis. 4. 4. Hardly no seasonal variations were found in the total free amino acid concentrations from both the total tissues and different organs. However, the individual amino acids showed clear seasonal changes in all tissues investigated. The greatest fluctuations were found for taurine and glycine. These amino acids showed an inverse relation to each other. 5. 5. Seasonal changes in the accumulation of end products of anaerobic metabolism and in the composition of the free amino acid pool were found in groups of mussels exposed to air for 48 h. The observed variations in propionate and alanine accumulation as well as other compiunds involved in anaerobic metabolism are discussed in relation to temperature and salinity.

On the role of strombine formation in the energy metabolism of adductor muscle of a sessile bivalve

Summary1.Intertidal rocky shore mussels (Mytilus edulis) were subjected for 24 h to aerial exposure and after returing them to aerated sea water, the adductor muscle was excised at various time intervals up to 50 h and analysed for alanine, aspartate, glutamate, ammonia, succinate, malate, pyruvate, octopine, strombine and malate. In addition pH,PO2 and ammonia of the blood taken from the adductor sinus were estimated at time intervals both during aerial exposure and recovery.2.It was observed that during the first 4 h of reimmersion the anaerobic end products were still formed, notably strombine (Fig. 1 a). It is argued that this is due to the fact that the energy demand in this period is too high to be met by respiration alone.3.Within the first 2 h after reimmersion there was full restoration ofPO2, an overshoot in pH (Figs. 2a, b) and the clearance of blood ammonia (Fig. 3) and of succinate in the adductor muscle. At the same time glutamate, alanine and aspartate levels increased. From 2 h onwards glutamate and alanine levels started to decrease.4.Within the first 4 h after reimmersion there was a much faster rate of formation of the pyruvate derivatives strombine, octopine and lactate when compared to the period of aerial exposure. Also pyruvate itself increased.5.In the first hours of reimmersion the adductor muscle fixes considerable amounts of free ammonia. This is regarded as an auxiliary mechanism for blood ammonia clearance, which complements excretion into the medium.6.It appears that anaerobic metabolism in the habitat of the sea mussel is involved not only in situations where oxygen uptake is blocked (natural anaerobiosis), but also when the energy demand is strongly increased (first hours of recovery). In the former condition alanine and succinate are the main end products, in the latter condition pyruvate derivatives accumulate.

The Influence of Seasonal Changes on Energy Metabolism in Mytilus edulis (L.). I. Growth Rate and Biochemical Composition in relation to Environmental Parameters and Spawning

ABSTRACT The growth rate and biochemical composition of Mytilus edulis (L.) were studied during an annual cycle. Mussels were selected on shell length every three weeks from the same population of a sublittoral musselbed in the Dutch Wadden Sea. The increases in shell length, wet weight and dry weight of mantle and total tissues are given. Seasonal changes in biochemical composition, i.e. variations in glycogen, protein and total lipids are discussed in relation to environmental factors and the reproductive cycle.

Further studies on the phylogenetic distribution of pyruvate oxidoreductase activities

Abstract 1. 1. The phylogenetic distribution of lactate, octopine, alanopine and strombine dehydrogenase activities (respectively, LDH, ODH, ADH and SDH) was examined in over 60 species from seven phyla and from three continents. 2. 2. The results confirm and extend previously published data. Consistencies of distribution are observed at the levels of phyla, class, order and family. 3. 3. Major observations include prominent SDH in the Porifera; LDH only in the Polyplacophera, Nudibranchia and Myidae (Mollusca) and nereid worms (Polychaeta); ODH and SDH in the marine pulmonate Melampus bidentatus (Basommatophora); high ADH to SDH ratios in marine gastropods; high ODH in active molluscs; and apparent SDH in the barnacle Lepas anatifera. 4. 4. The results are discussed in relation to theories of opine pathway evolution and the newly discovered tauropine and β-alanopine opine dehydrogenases.

Organ specific changes in energy metabolism due to anaerobiosis in the sea mussel Mytilus edulis (L).

Abstract 1. 1. Anaerobic energy metabolism was investigated in different organs of Mytilus edulis and the whole animal. 2. 2. Succinate accumulates to high levels in most organs but remains low in the hemolymph. 3. 3. After 16 hours propionate accumulation is observed in all organs. Experimental evidence is not sufficient yet to point out organs that produce more propionate than others. 4. 4. Acetate is a minor end product. 5. 5. Acetate and propionate are found in the hemolymph in amounts equal to those in the organs. 6. 6. Animals incubated in oxygen-free seawater accumulate more end products than animals exposed to air, in the form of volatile fatty acids that are excreted into the incubation water. 7. 7. Alanine and glutamine increase in the posterior adductor muscle. Aspartate decreases in the total animal, posterior adductor muscle and gills, while in the hemolymph decrease in alanine, asparagine, serine, threonine and proline are observed.

The influence of seasonal changes on energy metabolism in Mytilus edulise (L.).—III. Anaerobic energy metabolism

Abstract 1. 1. Seasonal changes in the accumulation of end products after 48 hr of exposure to air and in the composition of the free amino acid pool were studied in Mytilus edulis. 2. 2. The accumulation levels of succinate and acetate showed only weak seasonal changes. 3. 3. Conversion of succinate to propionate was high in summer and virtually zero in winter 4. 4. Alanine and most other free amino acids were present in relatively high concentrations in summer and early autumn and reached minimal values in winter and early spring. 5. 5. Exceptions were glutamate, aspartate and taurine, which showed hardly an season related changes and glycine, which changed inversely to the majority of the free amino acids. 6. 6. The anaerobic formation of alanine was inversely proportional to the endogenous concentration. 7. 7. The only other free amino acids affected by anaerobiosis were glutamate and aspartate, which respectively increased and decreased under these conditions.

The Influence of Seasonal Changes on Energy Metabolism in Mytilus edulis (L). II. Organ Specificity

ABSTRACT Seasonal changes in growth characteristics and content in energy substrates such as glycogen, lipids, proteins and free amino acids have been followed during a period of one year and a half in several organs of the common sea mussel: gills, mantle, posterior adductor muscle, hemolymph and the combined remaining tissues. The observed changes will be considered in relation to variations in environmental parameters like temperature, salinity and food availability. These data will be necessary when interpreting results from experiments designed to elucidate metabolic pathways in different organs during anaerobiosis.

THE INFLUENCE OF SEASONAL CHANGES ON ENERGY METABOLISM IN MYTILUS EDULIS (L.)

Publisher Summary Animals in the littoral zone are often submitted to strong fluctuations in environmental parameters because of tidal, circadian, and circannual changes in temperature, salinity, food availability, and reproductive activity. These changes have consequences for the aerobic and anaerobic energy metabolism of the animals. Distinct seasonal changes in the accumulation of propionate and alanine during this period are observed, while changes in succinate and acetate are either absent or unrelated to the time of the year. While propionate levels are high during the summer, this compound is virtually absent during winter. As succinate levels remain high, this cannot be because of a lack of precursor. Because temperature change concurrently with propionate, it seems probable that this is an important contributive factor in the observed changes. Changes in alanine because of anoxia are more or less opposite to those in propionate.

ON THE AEROBIC AND ANAEROBIC ENERGY METABOLISM OF Littorina SPECIES IN RELATION TO THE PATTERN OF INTERTIDAL ZONATION

Publisher Summary This chapter reviews the aerobic and anaerobic energy metabolism of Littorina species in relation to the pattern of intertidal zonation. In the intertidal area along the coast of Brittany, France, closely related Littorina species have their habitats at different levels of the shore. The species living at the low tide level zone are exposed to air for short periods only and may be protected against large variations in environmental conditions by Fucus or other sea weeds, stones, or rock pools. However, the species living near the high spring tide level may be exposed to air for weeks in an environment where thermal and desiccation stress are common. The species living in the upper part of the intertidal zone have a structural adaptation, that is, a reduced gill size, that makes the mantle cavity to assume a lung function. Thus, these species presumably are more adapted to breathing in air than their lower living relatives. Changes in salinity in the intertidal zone occur in estuaries or by rain fall. One of the strategies many molluscs exhibit to avoid harsh conditions is the withdrawal into the shell that can provoke anoxic conditions. The chapter discusses a study that was undertaken to find a possible relationship between the intertidal zonation pattern of five Littorina species, namely, L. nerotoides, L. rudis, L. nigrolineata, L, littorea, and L. obtusata, and the capabilities for oxygen uptake in water and air, and the capability to metabolize anaerobically. The results of the study showed no advantages for these species during exposure to air over the animals with a unmodified gill.

METABOLISM OF PYRUVATE DURING SHELL VALVE CLOSURE AND SUBSEQUENT RECOVERY IN THE SEA MUSSEL Mytilus edulis.

Publisher Summary This chapter discusses the metabolism of pyruvate during shell valve closure and subsequent recovery in the sea mussel Mytilus edulis. In the absence of oxygen, the adductor muscle of the sea mussel Mytilus edulis can metabolize pyruvate in at least five different ways. The formation of alanine is well established, but other options include the formation of lactate, N-(l-carboxyethyl)-alanine, alanopine, N-(l-carboxymethyl)-alanine, or strombine and octopine. Lactate is formed by direct reduction of pyruvate, and the others by reductive condensation of pyruvate with alanine, glycine, and arginine, respectively. Subtidal sea mussels were exposed to air for 48 h and allowed to recover. In the foot, stombine/alanopine accumulation continued during the first 3 h of recovery. In an experiment carried out on intertidal rocky shore mussels, in addition to biochemical analyses, pH and ρO2 determinations on blood taken from the adductor muscle sinus were carried out. The operation of anaerobic pathways, particularly the strombine pathway, during the first 3–4 h of recovery is probably required because during this period, energy demand will be high as animals return to an active state.