alphaB-crystallin maintains skeletal muscle myosin enzymatic activity and prevents its aggregation under heat-shock stress

Here, we provide functional and direct structural evidence that alphaB-crystallin, a member of the small heat-shock protein family, suppresses thermal unfolding and aggregation of the myosin II molecular motor. Chicken skeletal muscle myosin was thermally unfolded at heat-shock temperature (43 degrees C) in the absence and in the presence of alphaB-crystallin. The ATPase activity of myosin at 25 degrees C was used as a parameter to monitor its unfolding. Myosin retained only 65% and 8% of its ATPase activity when incubated at heat-shock temperature for 15 min and 30 min, respectively. However, 84% and 58% of the myosin ATPase activity was maintained when it was incubated with alphaB-crystallin under the same conditions. Furthermore, actin-stimulated ATPase activity of myosin was reduced by approximately 90%, when myosin was thermally unfolded at 43 degrees C for 30 min, but was reduced by only approximately 42% when it was incubated with alphaB-crystallin under the same conditions. Light-scattering assays and bound thioflavin T fluorescence indicated that myosin aggregates when incubated at 43 degrees C for 30 min, while alphaB-crystallin suppressed this thermal aggregation. Photo-labeled bis-ANS alphaB-crystallin fluorescence studies confirmed the transient interaction of alphaB-crystallin with myosin. These findings were further supported by electron microscopy of rotary shadowed molecules. This revealed that approximately 94% of myosin molecules formed inter and intra-molecular aggregates when incubated at 43 degrees C for 30 min. alphaB-Crystallin, however, protected approximately 48% of the myosin molecules from thermal aggregation, with protected myosin appearing identical to unheated molecules. These results are the first to show that alphaB-crystallin maintains myosin enzymatic activity and prevents the aggregation of the motor under heat-shock conditions. Thus, alphaB-crystallin may be critical for nascent myosin folding, promoting myofibrillogenesis, maintaining cytoskeletal integrity and sustaining muscle performance, since heat-shock temperatures can be produced during multiple stress conditions or vigorous exercise.     

Synthesis and Structure-Activity Relations of Tremerogen a-13, a Peptidal Sex Hormone of Tremella mesenterica

Myosin and reconstituted actomyosin free of regulatory proteins were mixed in 0.6 m KCl and 20 mm phosphate buffer at pH 6.0 and were tested quantitatively for thermally induced gelation properties by measuring the rigidity of the system at 65°C. Full enhancement of gelation was attained when the weight ratio of myosin-to-actomyosin was about 4. The addition of regulatory proteins to actomyosin could restore calcium sensitivity of the contractile system, but did not affect the heat-induced gelation of myosin in the presence of actomyosin, suggesting that regulatory proteins play no role in the heat-induced gelation of the system.

Neither the single and double headed subfragments, both capable of interacting with F-actin, nor the helical tail subfragments, devoid of the intracting site with F-actin, exhibited changes in thermogelling properties when mixed with F-actin. However, upon addition to F-actomyosin, the tail subfragments revealed a significant effect on the gelation of actomyosin, whereas the headed subfragments exerted no influence over gelation of the system. These results indicate that the enhancing effect of F-actin on the heat-induced gelation of myosin was brought about solely by the limited amount of F-actomyosin formed in the system, which acts as a cross-linker between the tail portion of bound and free myosin molecules.     

Electron microscope study of the effect of temperature on the length of the tail of the myosin molecule

The effect of temperature on the length of the tail of the myosin molecule has been studied by negative staining of molecules immobilized on carbon substrates at different temperatures. In buffers containing chloride as the principal anion, tail length was approximately constant up to 25 degrees C. Above this temperature, it shortened linearly with increasing temperature up to 42 degrees C, the highest temperature studied in this solvent. The amount of shortening per degree C was about 1.2 nm. A similar amount of shortening per degree C was seen in acetate-containing buffers up to 50 degrees C, but in this case it did not begin until the temperature exceeded about 40 degrees C. A large fraction of the observed shortening was localized in a region that lies roughly between the two positions in the tail where proteolysis results in production of short or long subfragment-2. Frequently, the tail had a different appearance in this region from elsewhere and could sometimes be seen to split into two strands that were separate but coiled around one another.     

Sterilization of ginseng using a high pressure CO2 at moderate temperatures

The aim of this study was to determine the feasibility of using high pressure CO2 for sterilization of Ginseng powder, as an alternative method to conventional techniques such as gamma-irradiation and ethylene oxide. The Ginseng sample used in this study was originally contaminated with fungi and 5 x 10(7) bacteria/g that was not suitable for oral use. This is the first time that high pressure CO2 has been used for the sterilization of herbal medicine to decrease the total aerobic microbial count (TAMC) and fungi. The effect of the process duration, operating pressure, temperature, and amount of additives on the sterilization efficiency of high pressure CO2 were investigated. The process duration was varied over 15 h; the pressure between 100 and 200 bar and the temperature between 25 and 75 degrees C. A 2.67-log reduction of bacteria in the Ginseng sample was achieved after long treatment time of 15 h at 60 degrees C and 100 bar, when using neat carbon dioxide. However, the addition of a small quantity of water/ethanol/H2O2 mixture, as low as 0.02 mL of each additive/g Ginseng powder, was sufficient for complete inactivation of fungi within 6 h at 60 degrees C and 100 bar. At these conditions the bacterial count was decreased from 5 x 10(7) to 2.0 x 10(3) TAMC/g complying with the TGA standard for orally ingested products. A 4.3 log reduction in bacteria was achieved at 150 bar and 30 degrees C, decreasing the TAMC in Ginseng sample to 2,000, below the allowable limit. However, fungi still remained in the sample. The complete inactivation of both bacteria and fungi was achieved within 2 h at 30 degrees C and 170 bar using 0.1 mL of each additive/g Ginseng. Microbial inactivation at this low temperature opens an avenue for the sterilization of many thermally labile pharmaceutical and food products that may involve sensitive compounds to gamma-radiation and chemically reactive antiseptic agents.     

Temperature and ionic strength dependence of the subunit interactions in vertebrate skeletal myosin. A comparison of the interaction between the alkali light and heavy chains of mammalian and avian myosin

The stability of the interaction of A1 in myosin and subfragment 1 isolated from fast-twitch mammalian and avian muscles with respect to temperature and ionic strength has been examined. This was done by determining the extent of exchange of the endogenous free A1 light chain into these proteins from the two species. Whereas the extent of exchange at 37 degrees C into mammalian S1, occurring after 60 min, is about 80% of the theoretically expected amount at physiological ionic conditions, the level of exchange observed with the avian S1 is significantly lower. However, close to the theoretical limit is observed for the avian S1 when exchange is done at 43 degrees C which is close to average avian body temperature. A similar dependence with temperature is observed in the case of exchanges into avian myosin. In the case of mammalian myosin, 50% of the theoretical exchange is observed at 37 degrees C under physiological ionic strength, whereas the level of exchange observed under these conditions with the avian protein is much lower in agreement with recent observations (Waller, G. S., and Lowey, S. (1985) J. Biol. Chem. 260, 14368-14373; Pastra-Landis, S. C., and Lowey, S. (1986) J. Biol. Chem. 261, 14811-14816). If, however, the exchanges are done at 43 degrees C in physiological ionic strength, significant extents of exchange can be observed in avian myosin. These results suggest that at physiological ionic and temperature conditions relevant for the source of myosin and S1 being investigated, the alkali light chains are in dynamic equilibrium between free and heavy chain associated states. Therefore, the failure to observe alkali light chain exchange in avian myosin at 37 degrees C appears to be related to the higher temperature stability of its interaction with the heavy chain.     

Volatile metabolites and external CO2 exchange of wheat cenoses under optimal conditions and thermal stress

The effects of elevated temperature (35 and 45 degrees C) on photosynthesis, respiration, and both the qualitative and quantitative compositions of volatile emissions (VE) of wheat (Triticum aestuvum L. cultivar 232) cenoses at light intensities of 70, 150, or 240 W/m2 of photosynthetically available radiation (PAR) were studied. At a PAR of 240 W/m2, the thermal stabilities of photosynthesis and respiration increased at 35 degrees C and decreased at 45 degrees C. Elevated temperatures nonuniformly changed the rates and direction of VE syntheses. In this process, the highest increase in VE evolution was observed at 70 W/m2; the lowest, at 240 W/m2 and 35 degrees C. In addition, the concentrations and composition of VE during the repair period differed from the initial values.     

Morphology and gelation of thermosensitive xyloglucan hydrogels

Galactose modified xyloglucan is a thermally reversible hydrogel that is increasingly used in the biomedical field due to the ease of altering the gelation time and temperature by modifying the galactose removal ratio. However there is little information concerning the morphology and rheological properties of the hydrogel under physiological conditions. Differential scanning microcalorimetry (DSmicroC) showed the thermal gelation process to occur over a broad temperature range (5-50 degrees C). The rheological properties of the hydrogels were investigated as a function of concentration, temperature and ionic strength. The final elastic moduli of the hydrogels increased with increases in concentration. Isothermal rheology suggests that the gelation occurred in two distinct stages, which was influenced by the solution media. Scanning electron microscopy (SEM) was used to characterize the morphology of the xyloglucan which were thermally gelled at 37 degrees C. The resultant morphology was strongly dependent on the concentration of the hydrogel. Strong hydrogels were only obtained at 3 wt.% at 37 degrees C, and the morphology characterized by an open 3-dimensional network, comprised of thin membranes. It is proposed that the first stage of the isothermal gelation is the formation and growth of the thin membranes, followed by the formation of a three dimensional network.     

Conformational stability of the myosin rod

Chymotryptic cleavage patterns of myosin rods from pig stomach, chicken gizzard, and rabbit skeletal muscle indicate that short (approximately 45 nm) heavy meromyosin subfragment 2 (SF2) is a consistent product of all three rods, whereas long (approximately 60 nm) SF2 is derived only from skeletal muscle myosin. Differential scanning calorimetry was used to follow the thermally induced melting transition of the rods and certain of their subfragments. In 0.12 M KCl, sodium phosphate buffer, pH 6.2-7.6, the light meromyosin (LMM) and SF2 domains of each rod had essentially identical conformational stabilities. Temperature midpoints for the melting transitions were 54-56 degrees C for the two smooth muscle myosin rods and 50-53 degrees C for the skeletal muscle myosin rod. In 0.6 M K Cl buffer, melting transitions for the smooth muscle myosin rods were essentially unchanged, but skeletal muscle myosin rods showed multiphase melting, with major transitions at 43 degrees C and 52 degrees C. The first of these was tentatively attributed to LMM, and the second to SF2. In 0.12 M K Cl buffer, the LMM transition was stabilised so that it superimposed on that of SF2. No melting was observed in any of the rods at physiological temperature. These results indicate that, excluding a possible but only narrow hinge region, the entire myosin rod has essentially uniform conformational stability at physiological pH and ionic strength, and thus that the contractile and elastic properties of the cross-bridge exist in the heavy meromyosin subfragment 1 (SF1) domains of the molecule.     

Chaperonin cpn60 from Escherichia coli protects the mitochondrial enzyme rhodanese against heat inactivation and supports folding at elevated temperatures.

The chaperonin protein cpn60 from Escherichia coli protects the monomeric, mitochondrial enzyme rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1) against heat inactivation. The thermal inactivation of rhodanese was studied for four different states of the enzyme: native, refolded, bound to cpn60 in the form of a binary complex formed from unfolded rhodanese, and a thermally perturbed state. Thermal stabilization is observed in a range of temperatures from 25 to 48 degrees C. Rhodanese that had been inactivated by incubation at 48 degrees C, in the presence of cpn60 can be reactivated at 25 degrees C, upon addition of cpn10, K+, and MgATP. A recovery of about 80% was achieved after 1 h of the addition of those components. Thus, the enzyme is protected against heat inactivation and kept in a reactivable form if inactivation is attempted using the binary complex formed between rhodanese folding intermediate(s) and cpn60. The chaperonin-assisted refolding of urea-denatured rhodanese is dependent on the temperature of the refolding reaction. However, optimal chaperonin assisted refolding of rhodanese observed at 25 degrees C, which is achieved upon addition of cpn10 and ATP to the cpn60-rhodanese complex, is independent of the temperature of preincubation of the complex, that was formed previously at low temperature. The results are in agreement with a model in which the chaperonin cpn60 interacts with partly folded intermediates by forming a binary complex which is stable to elevated temperatures. In addition, it appears that native rhodanese can be thermally perturbed to produce a state different from that achieved by denaturation that can interact with cpn60.     

Effect of altered ambient temperature on breathing in ponies

The objective was to determine the effect of moderate changes in ambient temperature (TA) on breathing and body temperature in ponies chronically exposed to a TA of 21 degrees C in the summer and 5 degrees C in the winter. Normal (n = 6) and chronic carotid body-denervated (n = 6, 1-2 yr) ponies were studied during 1) winter months over 3-4 days at 5 (control TA) and 23 degrees C and 2) summer months over 2-4 days at 21 (control TA), 30, and 12 degrees C. Neither rectal nor arterial temperature changed with any alteration of TA (P greater than 0.10). Skin temperature (Tsk) always changed by 2-4 degrees C in the same direction as changes in TA (P less than 0.01), and Tsk was the only variable that differed between summer and winter control TA. While breathing room air 24-48 h after TA was altered, pulmonary ventilation (VE) and breathing frequency (f) were approximately 100 and 300%, respectively, above control with elevated TA and approximately 25-50% below control with reduced TA (P less than 0.01). Changes in f were closely related to changes in Tsk. Tidal volume (VT) changed inversely with changes in TA. Generally, while breathing room air, arterial PCO2 (Paco2) did not change from control during the first 48 h of altered TA. In studies when inspired CO2 was elevated VT increased by the same amount at all TA; f increased at low and control TA but decreased at elevated TA; and VE and Paco2 both increased relatively less at elevated TA, but the VE-Paco2 slope was independent of TA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Unique gelation behavior of cellulose in NaOH/urea aqueous solution

A transparent cellulose solution was prepared by mixing 7 wt % NaOH with 12 wt % urea aqueous solution which was precooled to below -10 degrees C and which was able to rapidly dissolve cellulose at ambient temperature. The rheological properties and behavior of the gel-formed cellulose solution were investigated by using dynamic viscoelastic measurement. The effects of temperature, time, cellulose molecular weight, and concentrations on both the shear storage modulus (G') and the loss modulus (G") were analyzed. The cellulose solution having a viscosity-average molecular weight (M(eta)) of 11.4 x 10(4) had its sol-gel transition temperature decreased from 60.3 to 30.5 degrees C with an increase of its concentration from 3 to 5 wt %. The gelation temperature of a 4 wt % cellulose solution dropped from 59.4 to 30.5 degrees C as the M(eta) value was increased from 4.5 x 10(4) to 11.4 x 10(4). Interestingly, at either higher temperature (above 30 degrees C), or lower temperature (below -3 degrees C), or for longer gelation time, gels could form in the cellulose solutions. However, the cellulose solution remains a liquid state for a long time at the temperature range from 0 to 5 degrees C. For the first time, we revealed an irreversible gelation in the cellulose solution system. The gel having been formed did not dissolve even when cooled to the temperature of -10 degrees C, at which it was dissolved previously. Therefore, this indicates that either heating or cooling treatment could not break such stable gels. A high apparent activation energy (E(a)) of the cellulose solution below 0 degrees C was obtained and was used to explain the gel formation under the cooling process.     

Action of ascorbic acid on a myosin molecule derived from carp

The influence of L-ascorbic acid at 40 degrees C incubation on the subfragment-1 and rod regions, prepared by chymotryptic digestion of myosin, and myosin was investigated by SDS-polyacrylamide gel electrophoresis and transmission electron microscopy respectively. It was observed that L-ascorbic acid acted more readily on the subfragment-1 region of myosin. Further, circular dichroism measurement indicated that L-ascorbic acid did not affect the structure of myosin. These results suggest that L-ascorbic acid acts more readily on the myosin subfragment-1 region and promotes the gelation of myosin without producing a conformational change in this protein.     

On the flexibility of myosin in solution.

Rabbit skeletal muscle myosin from the same rabbit was prepared by two different methods, and then purified by either Sephadex or hydroxylapatite chromatography. The resulting myosin samples were analyzed in 2-10 mM sodium pyrophosphate solutions at pH 9 using transient electric birefringence. The birefringence decay signals were fitted using a Fortran program called DISCRETE and two relaxation times, 49.7 +/- 5.6 and 11.2 +/- 2.5 microseconds, were determined. These relaxation times were independent of the method of myosin preparation, the method of myosin purification, the concentration of sodium pyrophosphate between 2 and 10 mM, the concentration of myosin between 0.08 and 1.59 mg/mL, and the temperature between 4.0 and 20.0 degrees C, after correction to 20.0 degrees C. The longer relaxation time is consistent with a rigid, linear myosin molecule. The shorter relaxation time is consistent with myosin that has a completely flexible hinge region in the myosin tail. Both relaxation times are inconsistent with the previously reported single relaxation time of myosin obtained by fitting the birefringence decay data to only 90% of the decay signal. By forcing some of the birefringence decay data in the presence work to fit 90% of the decay signal with a single relaxation time, approximately the same relaxation time as previously reported was obtained.     

Kinetics of pressure inactivation at subzero and elevated temperature of lipoxygenase in crude green bean (Phaseolus vulgaris L.) extract

Lipoxygenase (LOX) in crude green bean extract was irreversibly inactivated by pressure treatments combined with subzero or elevated temperature. LOX inactivation was described accurately assuming a first-order reaction. In the entire pressure-temperature domain studied (200 to 700 MPa and -10 to 60 degrees C), an increase in pressure at constant temperature enhanced the LOX inactivation rate, whereas at constant pressure, an increase in reaction rate was obtained by either increasing or decreasing temperature at 20 degrees C. At elevated pressure, LOX exhibited the greatest stability around 20 degrees C. Also the pressure dependence of the inactivation rate constants for LOX was the highest around 20 degrees C. On the basis of the estimated LOX inactivation rate constants, an iso-rate contour diagram as a function of pressure and temperature was constructed, and an empirical mathematical model describing the combined pressure-temperature dependence of the LOX inactivation rate constants was formulated.     

The contractile basis of amoeboid movement: V. The control of gelation, solation, and contraction in extracts from dictyostelium discoideum

Motile extracts have been prepared from Dictyostelium discoideum by homogenization and differential centrifugation at 4 degrees C in a stabilization solution (60). These extracts gelled on warming to 25 degrees Celsius and contracted in response to micromolar Ca++ or a pH in excess of 7.0. Optimal gelation occurred in a solution containing 2.5 mM ethylene glycol-bis (β-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA), 2.5 mM piperazine-N-N'-bis [2-ethane sulfonic acid] (PIPES), 1 mM MgC1(2), 1 mM ATP, and 20 mM KCI at ph 7.0 (relaxation solution), while micromolar levels of Ca++ inhibited gelation. Conditions that solated the gel elicited contraction of extracts containing myosin. This was true regardless of whether chemical (micromolar Ca++, pH >7.0, cytochalasin B, elevated concentrations of KCI, MgC1(2), and sucrose) or physical (pressure, mechanical stress, and cold) means were used to induce solation. Myosin was definitely required for contraction. During Ca++-or pH-elicited contraction: (a) actin, myosin, and a 95,000-dalton polypeptide were concentrated in the contracted extract; (b) the gelation activity was recovered in the material sqeezed out the contracting extract;(c) electron microscopy demonstrated that the number of free, recognizable F-actin filaments increased; (d) the actomyosin MgATPase activity was stimulated by 4- to 10-fold. In the absense of myosin the Dictyostelium extract did not contract, while gelation proceeded normally. During solation of the gel in the absense of myosin: (a) electron microscopy demonstrated that the number of free, recognizable F- actin filaments increased; (b) solation-dependent contraction of the extract and the Ca++-stimulated MgATPase activity were reconstituted by adding puried Dictyostelium myosin. Actin purified from the Dictyostelium extract did not gel (at 2 mg/ml), while low concentrations of actin (0.7-2 mg/ml) that contained several contaminating components underwent rapid Ca++ regulated gelation. These results indicated : (a) gelation in Dictyostelium extracts involves a specific Ca++-sensitive interaction between actin and several other components; (b) myosin is an absolute requirement for contraction of the extract; (c) actin-myosin interactions capable of producing force for movement are prevented in the gel, while solation of the gel by either physical or chemical means results in the release of F-actin capable of interaction with myosin and subsequent contraction. The effectiveness of physical agents in producting contraction suggests that the regulation of contraction by the gel is structural in nature.     

Studies on Tetrahymena membranes. Palmitoyl-coenzyme a desaturase, a possible key enzyme for temperature adaptation in Tetrahymena microsomes.

(1) Microsomes from a thermotolerant Tetrahymena NT-1 catalyze the conversion of palmitoyl-CoA to palmitoleate. (2) Palmitoyl-CoA desaturase enzyme requires molecular oxygen and NADH or NADPH as cofactor and its activity is inhibited by cyanide. A pH optimum range 7.0--7.3 is observed. (3) There is a clear break at 30 degrees C and a slight bend around 15 degrees C in the Arrhenius plots of palmitoyl-CoA desaturase activity. (4) After quenching from 39.5 degrees C, at 26 degrees C microsomal membranes show small particle-free areas, when examined by freeze-fracture electron microscopy, indicating the onset of phase separation. Larger smooth areas devoid of membrane-intercalated particles are observed in microsomes at 23 and 15 degrees C. The results support evidence that the thermally induced transition of desaturase enzyme activity in related to the altered membrane properties due to temperature change.     

Effect of water on the molecular mobility of elastin

Purified and hydrated elastin is studied by both thermal and dielectric techniques to have insight into the chain dynamics of this protein. By differential scanning calorimetry, the glassy behavior of elastin is highlighted; the glass transition temperature (T(g)) of elastin is found to be widely dependent on hydration, falling from 200 degrees C in the dehydrated state to 30 degrees C for 30% hydration. A limit of T(g) at around 0 degrees C is found when crystallizable water is present in the system, that is, when the formation of ice prevents motions of some 10 nm along the polypeptidic chains. The technique of thermally stimulated currents, carried out in the -180 to 0 degrees C temperature range, is useful to detect localized motions. In this case, too, the localized motions vary considerably according to hydration: a first relaxation mode is observed at -145 degrees C and it is associated with the reorientation of crystallizable water in ice I; a second relaxation mode, more complex and cooperative, occurs at around -80 degrees C and could be attributed to the complex constituted by the dipolar groups of the polypeptidic chain and noncrystallizable water, behaving as a glassy system.     

Body temperature regulation in the rat

In loosely-restrained adult conscious rats exposed to stepwise changes in ambient temperature (T(a)) from 25 to 5 degrees C or from 20 to 35 degrees C, we have recorded body and tail temperatures, metabolic rate (VO(2)), shivering and ventilation (V). It was found that VO(2) and V vary with T(a) and show a nadir for a T(a) of 30 degrees C whereas shivering starts at 20 degrees C and increases progressively with cold exposure. T(tail) follows changes in T(a) whereas T(body) decreases slightly in cold and increases markedly in warm exposure. These results suggest that the control of T(body) interacts with the control of breathing in order to increase VO(2) during cold exposure and to facilitate evaporative respiratory heat dissipation during warm exposure.     

Structural changes in the actin-myosin cross-bridges associated with force generation induced by temperature jump in permeabilized frog muscle fibers.

Structural changes induced by Joule temperature jumps (T-jumps) in frog muscle fibers were monitored using time-resolved x-ray diffraction. Experiments made use of single, permeabilized fibers that were fully activated after slight cross-linking with 1-ethyl-3-[3-dimethylamino)propyl]carbodiimide to preserve their structural order. After T-jumps from 5-6 to approximately 17 degrees C and then on to approximately 30 degrees C, tension increased by a factor of 1.51 and 1.84, respectively, whereas fiber stiffness did not change with temperature. The tension rise was accompanied by a decrease in the intensity of the (1, 0) equatorial x-ray reflection by 15 and 26% (at approximately 17 and approximately 30 degrees C) and by an increase in the intensity of the M3 myosin reflection by 20% and 41%, respectively. The intensity of the (1,1) equatorial reflection increased slightly. The peak of the intensity on the 6th actin layer line shifted toward the meridian with temperature. The intensity of the 1st actin layer line increased from 12% (of its rigor value) at 5-6 degrees C to 36% at approximately 30 degrees C, so that the fraction of the cross-bridges labeling the actin helix estimated from this intensity increased proportionally to tension from approximately 35% at 5-6 degrees C to approximately 60% at approximately 30 degrees C. This suggests that force is generated during a transition of nonstereo-specifically attached myosin cross-bridges to a stereo-specific binding state.     

Plasticity of myosin heavy chain expression with temperature acclimation is gradually acquired during ontogeny in the common carp (Cyprinus carpio L.)

Common carp (Cyprinus carpio L.) were reared from hatching until 61 mm total length (TL) at 21 degrees C. At 14 weeks and 20 weeks post-hatch, corresponding to initial lengths of 30 mm and 44 mm respectively, fish were acclimated to 10 degrees C using a rate of cooling of 1 degrees C per day. A statistical model was used to compare the time course in the change of white muscle myofibrillar ATPase activity with temperature acclimation. The myosin heavy chain (MHC) composition of white muscle myofibrils was investigated using peptide mapping. A significant increase in myofibrillar ATPase activity was observed after 2-3 weeks in the 44 mm group, but not until 4-5 weeks in the 30 mm group. when they had reached 37 mm TL. The MHC banding pattern of 120 mm TL fish acclimated to 10 degrees C or 21 degrees C for a minimum of 6 weeks were distinct from each other. The MHC peptide map characteristic of 10-degrees C-acclimated fish was not observed in individuals less than 37 mm length. We therefore conclude that the capacity to alter the composition and properties of myofibrils with cold acclimation is acquired in juvenile carp at around 37 mm TL.