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1.
ISOLATION AND REACTIVATION OF THE AXOSTYLE : Evidence for a Dynein-like ATPase in the Axostyle 总被引:11,自引:11,他引:0
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The contractile axostyle is a ribbon-shaped organelle present in certain species of flagellates found in the hindgut of wood eating insects. This organelle propagates an undulatory wave whose motion, like flagella and cilia, is related to microtubules. Unlike the axoneme of cilia and flagella, however, the axostyle is composed of singlet microtubules linked together in parallel rows. Axostyles were isolated from Cryptocercus gut protozoa with Triton X-100. Normal motility of the isolated axostyle could be restored with adenosine triphosphate (ATP); the specific conditions necessary for this reactivation were essentially identical with those reported for the reactivation of isolated flagella or whole sperm. ATPase activity of the isolated axostyle was comparable to the values reported for ciliary or flagellar axonemes. The axostyle was reasonably specific for ATP. Most of the proteins of the isolated axostyle comigrated with proteins of the ciliary axoneme on sodium dodecyl sulfate (SDS) polyacrylamide gels (i e. equivalent molecular weights). These included the following: the higher molecular weight component of dynein, tubulin, linkage protein (nexin), and various secondary proteins. Evidence for dynein in the axostyle is presented and a model proposed to explain how repeated propagated waves can be generated. 相似文献
2.
We previously described a remarkable type of cell motility that provided direct, visual evidence for the fluid nature of cell membranes. The movement involved continual, unidirectional rotation of one part of a protozoan, including the plasma membrane and cytoplasmic organelles, in relation to a neighbouring part. The cell membrane in the 'shear zone' appeared continuous with that of the rest of the cell. The rotary motor consisted, at least in part, of a non-contractile, microtubular axostyle which extended centrally through the cell. The protozoan was a devescovinid flagellate found in the hindgut of a Florida termite. In this paper, we have confirmed earlier reports of this type of motility in other kinds of devescovinids from Australian termites. By demonstrating continuity of the plasma membrane in the shear zone of the Australian devescovinids as well, we have obtained additional examples that provide direct, visual evidence for fluid membranes. A comparative analysis of rotational motility in various devescovinids revealed 2 different kinds of rotary mechanisms. Hyperdevescovina probably have an internal motor, in which one part of the cell exerts forces against another part, as in the Florida termite devescovinid. Devescovina species, on the other hand, have an external motor, in which flagellar and/or papillar movements exert forces against the surrounding medium. The structure of the axostyle in different devescovinids was compared, and its role in rotational motility discussed with respect to the behavioural data. 相似文献
3.
《The Journal of cell biology》1982,94(3):697-709
A devescovinid flagellate from termites exhibits rapid gliding movements only when in close contact with other cells or with a substrate. Locomotion is powered not by the cell's own flagella nor by its remarkable rotary axostyle, but by the flagella of thousands of rod bacteria which live on its surface. That the ectosymbiotic bacteria actually propel the protozoan was shown by the following: (a) the bacteria, which lie in specialized pockets of the host membrane, bear typical procaryotic flagella on their exposed surface; (b) gliding continues when the devescovinid's own flagella and rotary axostyle are inactivated; (c) agents which inhibit bacterial flagellar motility, but not the protozoan's motile systems, stop gliding movements; (d) isolated vesicles derived from the surface of the devescovinid rotate at speeds dependent on the number of rod bacteria still attached; (e) individual rod bacteria can move independently over the surface of compressed cells; and (f) wave propagation by the flagellar bundles of the ectosymbiotic bacteria is visualized directly by video-enhanced polarization microscopy. Proximity to solid boundaries may be required to align the flagellar bundles of adjacent bacteria in the same direction, and/or to increase their propulsive efficiency (wall effect). This motility-linked symbiosis resembles the association of locomotory spirochetes with the Australian termite flagellate Mixotricha (Cleveland, L. R., and A. V. Grimstone, 1964, Proc. R. Soc. Lond. B Biol. Sci., 159:668-686), except that in our case propulsion is provided by bacterial flagella themselves. Since bacterial flagella rotate, an additional novelty of this system is that the surface bearing the procaryotic rotary motors is turned by the eucaryotic rotary motor within. 相似文献
4.
5.
The flagellar movement of intact ejaculated ram sperm, and of demembranated models reactivated with ATP, has been studied using high-speed, high-resolution video microscopy. Intact sperm attached to the coverslip by their heads had an average beat frequency of 20.9 Hz and an average wave amplitude of 20.2 micron. There was little difference in the beat frequency or waveform of these sperm and sperm swimming freely near the coverslip or captured by their heads with a micropipette and held far from the coverslip, indicating that the flagellar waveform of ram sperm is relatively resistant to distortion as a result of immobilization of the head or proximity to a surface. The beat envelope was nearly planar as determined by observations of free-swimming sperm and sperm captured by their head and oriented so they were beating either parallel or perpendicular to the plane of focus. The effect of various conditions for demembranation and reactivation of the sperm were examined. Treatment of sperm with 0.2% Triton X-100 removed most of their plasma membrane. Under optimal conditions, nearly 100% of the demembranated sperm reactivated at MgATP2- concentrations ranging from approximately 4 microM to approximately 20 mM. From approximately 1 mM to approximately 10 mM MgATP2-, their beat pattern closely resembled that of intact sperm; beat frequency depended on MgATP2- concentration. Percent motility was maximal between pH 7.5 and 8.0 and decreased sharply below pH 7.0 and above pH 8.5. The addition of 50 microM cAMP to the reactivation medium had no effect on percent motility or the beat pattern and did not accelerate the initiation of movement. 相似文献
6.
C H Yeung 《Journal of reproduction and fertility》1987,81(1):195-203
Hamster spermatozoa collected from the caput and cauda epididymidis were washed, diluted in a medium containing Triton X-100 to dissolve the cell membrane and reactivated with various concentrations of MgSO4 and ATP. Stepwise increase in the concentrations of free ATP4- from 0.08 to 1.1 mM at constant concentrations of MgATP2- caused a dose-dependent delay of reactivation but the maximal percentage of motile spermatozoa was inhibited only at 1.1 mM. The inhibitory effect on caput spermatozoa was greater than that on cauda spermatozoa. When concentrations of ATP4- were fixed at 0.2 mM, 2.9 mM-MgATP2- suppressed the reactivation of cauda spermatozoa. When compared to 0.9 mM-MgATP2-, reactivation of caput spermatozoa was delayed at 1.9 mM and almost completely blocked by 2.9 mM-MgATP2-. Inhibition of cauda sperm reactivation by ATP4- and MgATP2- were both prevented by the presence of trypsin (50 ng/ml). Incubation of cauda spermatozoa in the reactivation medium for 1 and 2 min before the addition of ATP progressively reduced the inhibitory effect of ATP4-; inhibition by MgATP2- was reduced to a lesser extent. Addition of 100 microM-cyclic AMP to the medium abolished the delay of reactivation by ATP4- but not that by MgATP2-. Before reactivation occurred, inhibitory concentrations of ATP4- and MgATP2- both induced large-angle coiling of sperm tails but in opposite direction to each other with reference to the asymmetric sperm head. The results suggest that free-ATP4- and superoptimal concentrations of MgATP2- inhibit flagellar movement by different mechanisms. 相似文献
7.
Axokinin phosphorylation by cAMP-dependent protein kinase is sufficient for activation of sperm flagellar motility 总被引:4,自引:3,他引:1
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Using a selective inhibitor of cAMP-dependent protein kinase, N-[2(methylamino)ethyl]-5-isoquinolinesulfonamide (H-8), the requirement for cAMP-dependent phosphoproteins in the initiation of dog sperm flagellar motility was examined. H-8 inhibited motility of live as well as reactivated sperm in a dose-dependent manner. The half-maximal inhibition of reactivated motility (32 microM) paralleled the inhibition of pure catalytic subunit of cAMP-dependent protein kinase (50 microM) measured under the same conditions. H-8 inhibited protein phosphorylation both in whole models and in isolated Nonidet P-40 (NP-40) extracts of sperm. Axokinin, the heat-stable NP-40-soluble protein whose phosphorylation is required for flagellar reactivation, represented 97% of the de novo phosphate incorporation in the NP-40 extract after stimulation by cAMP. 500 microM H-8 inhibited axokinin phosphorylation by 87%. When sperm were reactivated in the presence of up to 5 mM H-8 with NP-40 extract that had been prephosphorylated with cAMP-dependent protein kinase, then neither cAMP nor cAMP-dependent protein kinase activity was required for full flagellar reactivation. If sperm were rendered completely immotile by pretreatment with H-8, then the resulting model remained immotile in the continued presence of H-8 unless prephosphorylated axokinin was added. These results suggest that phosphorylated axokinin is not only required for flagellar reactivation but is sufficient as well. 相似文献
8.
Kamiya R 《Methods (San Diego, Calif.)》2000,22(4):383-387
Flagellar mutants of Chlamydomonas have greatly contributed to our understanding of the function of axonemes and axonemal dyneins. An important step in studying mutants is to correlate the molecular and structural defects in the axoneme with motility. This is not always easy, however, partly because it is often necessary to quantify axonemal motility by measuring the cell's swimming velocity, the flagellar beat frequency, or flagellar waveform in a number of cells or axonemes. To skip this time-consuming step, a quick method for measuring the average flagellar beat frequency in a population of cells is developed based on fast Fourier transform (FFT) analysis of the vibration of cell bodies. This method yields the average beat frequency within 10-60 s and has been used as a powerful tool for identifying mutants lacking various dynein species. It is also particularly useful for studies analyzing detergent-extracted cell models under various reactivation conditions. 相似文献
9.
The mitochondrion of sea urchin sperm is located at the base of the sperm head, and the flagellum extends from the mitochondrion for approximately 40 microM. These sperm have two known flagellar, non-mitochondrial, enzymatic systems to rephosphorylate ADP. The first involves the phosphocreatine shuttle, where flagellar creatine kinase (Sp-CK) uses phosphocreatine to rephosphorylate ADP. The second system, studied in this report, is adenylate kinase (Sp-AK), which uses 2 ADP to make ATP + AMP. Cloning of Sp-AK shows that, like Sp-CK, Sp-AK has three catalytic domains. Sp-AK localizes along the entire flagellum, and most of it is tightly bound to the axoneme. Sp-AK activity and flagellar motility were studied using demembranated sperm. The specific Sp-AK inhibitor Ap5A blocks enzyme activity with an IC50 of 0.41 microM. In 1 mm ADP, flagella reactivate motility in 5 min; 1 microM Ap5A completely inhibits this reactivation. No inhibition of motility occurs in Ap5A when 1 mm ATP is added to the reactivation buffer. The pH optimum for Sp-AK is 7.7, an internal pH at which sperm are fully motile. The pH optimum for Sp-CK is 6.7, an internal pH at which sperm are immotile. In isolated, detergent-permeabilized flagella, assayed at pH 7.6, the Km for Sp-AK is 0.32 mm and the Vmax is 2.80 microM ATP formed/min/mg of protein. When assayed at pH 7.6, the Sp-CK Km is 0.25 mm and the Vmax 5.25. At the measured in vivo concentrations of ADP of 114 microM, at pH 7.6, the axonemal Sp-AK could contribute approximately 31%, and Sp-CK 69%, of the total non-mitochondrial ATP synthesis associated with the demembranated axoneme. Thus, Sp-AK could contribute substantially to ATP synthesis utilized for motility. Alternatively, Sp-AK could function in the removal of ADP, which is a potent inhibitor of dynein ATPase. 相似文献
10.
Regulation of activation state and flagellar wave form in epididymal rat sperm: evidence for the involvement of both Ca2+ and cAMP 总被引:1,自引:0,他引:1
Rat sperm from the cauda epididymis exhibit increased motility, longevity, and a distinct circular pattern of flagellar curvature in response to 5 mM procaine-HCl or 0.1 mM 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate (TMB-8), reagents that are thought to play a role in the immobilization of free cellular calcium. Triton X-100-extracted sperm models will exhibit the same pattern of motility and curvature as procaine- or TMB-8-activated cells, but only when calcium is removed by a strong chelating agent, and in the presence of cAMP (3 microM). Demembranated sperm models produced from epididymal rat sperm are quiescent unless cAMP is added. In these sperm models, the presence or absence of free calcium mediates a transition in flagellar curvature. The increased activity of the procaine-treated intact cells was not accompanied by a change in cellular ATP content, nor was ATP availability the limiting factor in the quiescent sperm. Therefore, the increased motility produced by procaine is probably mediated by a fall in free intracellular Ca2+ accompanied by a rise in cAMP. Our finding that calcium controls the curvature of sperm flagella may explain altered patterns of flagellar beating, such as the hyperactivated motility that sperm exhibit in the female reproductive tract. 相似文献
11.
12.
Calcium regulation of flagellar curvature and swimming pattern in triton X-100--extracted rat sperm 总被引:3,自引:0,他引:3
Free Ca2+ changes the curvature of epididymal rat sperm flagella in demembranated sperm models. The radius of curvature of the flagellar midpiece region was measured and found to be a continuous function of the free Ca2+ concentration. Below 10(-7) M free Ca2+, the sperm flagella assumed a pronounced curvature in the same direction as the sperm head. The curvature reversed direction at 2.5 x 10(-6) M Ca2+ to assume a tight, hook-like bend at concentrations of 10(-5) to 10(-4) M free Ca2+. Sodium vanadate at 2 x 10(-6) M blocked flagellar motility, but did not inhibit the Ca2+-mediated change in curvature. Nickel ion at 0.2 mM and cadmium ion at 1 microM interfered with the transition and induced the low Ca2+ configuration of the flagellum. The forces that maintain the Ca2+-dependent curvature are locally produced, as dissection of the flagella into segments did not significantly alter the curvature of the excised portions. Irrespective of the induced pattern of curvature, the sperm exhibited coordinated, repetitive flagellar beating in the presence of ATP and cAMP. At 0.3 mM ATP the flagellar waves propagated along the principal piece while the level of free Ca2+ controlled the overall curvature. When Ca2+-treated sperm models with hooked midpieces were subjected to higher concentrations of ATP (1-5 mM), some cells exhibited a pattern of movement similar to hyperactivated motility in capacitated live sperm. This type of motility involved repetitive reversals of the Ca2+-induced bend in the midpiece, as well as waves propagated along the principal piece. The free Ca2+ available to the flagellum therefore appeared to modify both the pattern of motility and the flagellar curvature. 相似文献
13.
Hyperactivated motility of bull sperm is triggered at the axoneme by Ca2+ and not cAMP 总被引:3,自引:0,他引:3
Hyperactivated motility, a swimming pattern of mammalian sperm in the oviduct, is essential for fertilization in vivo. It is characterized by high-amplitude flagellar waves and, usually, highly asymmetrical flagellar beating. It had been suggested, but not tested, that Ca2+ and cAMP switch on hyperactivation by directly affecting the flagellar axoneme. In this study, the direct affects of these agents on the axoneme were tested by using detergent-demembranated bull sperm. As confirmed by TEM, treatment of sperm with 0.2% Triton X-100 disrupted the plasma, acrosomal, and inner mitochondrial membranes, leaving axonemes intact. In the presence of 2 mM ATP, the percentage of reactivated sperm that were hyperactivated increased to 80% when free Ca2+ was increased from 50 to 400 nM. The effect of the Ca2+ in this range was to increase beat asymmetry by increasing the curvature of the principal bend. No additional increases were observed above 400 nM free Ca2+, but motility was suppressed at 1 mM. The ability of Ca2+ to produce hyperactivation depended on ATP availability, such that more ATP was required to produce the high amplitude flagellar bends characteristic of hyperactivated motility than to produce activated motility. Cyclic AMP was not required for reactivation, nor for hyperactivation. Production of hyperactivated motility also required an alkaline environment (pH 7.9-8.5). These results suggest that, provided sufficient ATP is present and pH is sufficiently alkaline, Ca2+ switches on hyperactivation by enabling curvature of the principal bends to increase. 相似文献
14.
Regulation of sperm flagellar movement by protein phosphorylation and dephosphorylation 总被引:2,自引:0,他引:2
H Murofushi K Ishiguro D Takahashi J Ikeda H Sakai 《Cell motility and the cytoskeleton》1986,6(2):83-88
Flagellar motility of Triton models of sea urchin spermatozoa was reactivated by cyclic AMP-dependent protein kinase and a protein factor, termed motility activator, both of which were prepared from the detergent-extract of sea urchin spermatozoa. It was shown that phosphorylation of the motility activator by the protein kinase is necessary for the reactivation of flagellar motility [Ishiguro et al, J. Cell Biol. 92:777-782, 1982; Murofushi et al, in "Biological Functions of Microtubules and Related Structures," Academic Press, 1982]. Reactivating factor was also detected in a KCl-extract of the axoneme fraction devoid of the detergent-extractable materials. The activity of this factor was also cyclic AMP- and protein kinase-dependent. Furthermore, when freshly prepared Triton models were treated with phosphoprotein phosphatase prepared from bovine cardiac muscle, the flagellar motility was drastically suppressed. This inhibition of the motility was partially recovered by the addition of cyclic AMP and protein kinase to the phosphatase-treated models. 相似文献
15.
Ishijima S Iwamoto T Nozawa S Matsushita K 《Molecular reproduction and development》2002,63(4):459-463
Electron microscopic examination of the spermatozoa from a man suffering from asthenozoospermia (poor or low sperm motility) showed that approximately 92% of the sperm flagella lacked central pair microtubules but possessed dynein arms and radial spokes while a small percentage of the spermatozoa had complete flagella. The characteristics of the motor apparatus of the spermatozoa and the effects of caffeine on the sperm motility were examined, as were the reactivation of demembranated spermatozoa and the sliding of doublet microtubules. Almost all spermatozoa were immotile in a Tyrode solution while only a small percentage of spermatozoa showed slow forward movement or feeble flagellar vibration, whereas addition of caffeine to the sperm suspension induced forward swimming of approximately half of the spermatozoa. The reactivation of demembranated spermatozoa with MgATP(2-) could not succeed because of disintegration of the demembranated flagella. However, when the demembranated spermatozoa were exposed to MgATP(2-) and then treated with elastase, the microtubular doublets of approximately half the number of the flagella slid from the end or middle of the flagella. These results suggest that the motor apparatus in the sperm flagella that lack the central pair microtubules is functionally assembled and intrinsically capable of undergoing flagellar movement but not strong enough to beat normally. 相似文献
16.
Mechanochemical coupling in the relaxation of rigor-wave sea urchin sperm flagella 总被引:4,自引:4,他引:0
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The relaxation (straightening) of flagellar rigor waves, which is known to be induced by micromolar ATP concentrations was investigated with respect to its dependence on the binding and hydrolysis of ATP. Flagellar rigor waves were formed by the dilution of demembranated, reactivated sea urchin (Lytechinus pictus) spermatozoa into ATP-free buffer. Relaxation in response to nucleotide was quantitated by measuring theta, the mean flagellar bend angle per sperm; this novel assay permitted determination of the rate of relaxation. It was found that (a) the rate of flagellar relaxation induced by 4 X 10(-6) M ATP was inhibited 80% by vanadate concentrations of 3 X 10(-6) M and above; (b) of 16 hydrolyzable and nonhydrolyzable nucleotide di-, tri-, and tetraphosphates tested, only three, each of which was hydrolyzed by the flagellar axonemal ATPase activity (ATP, dATP, and epsilon-ATP) were also capable of effecting relaxation; (c) several hundred ATP molecules were estimated to be hydrolyzed by each dynein of ATP hydrolysis, which defines the efficiency of ATP utilization, increased 30-fold as the ATP relaxation depends on ATP hydrolysis; (b) because it depends on ATP hydrolysis, flagellar relaxation is an inappropriate model system for investigating the role of ATP binding in the mechanochemical cycle of dynein; and (c) the efficiency of mechanochemical coupling in flagellar motility is an ATP-dependent phenomenon. A general model of relaxation is proposed based on active microtubule sliding. 相似文献
17.
C Dreanno J Cosson M Suquet C Cibert C Fauvel G Dorange R Billard 《Journal of reproduction and fertility》1999,116(1):113-125
Sea bass spermatozoa are maintained immotile in the seminal fluid, but initiate swimming for 45 s at 20 degrees C, immediately after dispersion in a hyperosmotic medium (1100 mOsm kg-1). The duration of this motile period could be extended by a reduction of the amplitude of the hyperosmotic shock. Five seconds after the initiation of motility, 94.4 +/- 1.8% of spermatozoa were motile with a swimming velocity of 141.8 +/- 1.2 microns s-1, a flagellar beat frequency of 60 Hz and a symmetric type of flagellar swimming, resulting in linear tracks. Velocity, flagellar beat frequency, percentage of motile cells and trajectory diameter decreased concomitantly throughout the swimming phase. After 30 s of motility, the flagellar beat became asymmetric, leading to circular trajectories. Ca2+ modulated the swimming pattern of demembranated spermatozoa, suggesting that the asymmetric waves produced by intact spermatozoa after 30 s of motility were induced by an accumulation of intracellular Ca2+. Moreover, increased ionic strength in the reactivation medium induced a dampening of waves in the distal portion of the flagellum and, at high values, resulted in an arrest of wave generation in demembranated spermatozoa. In non-demembranated cells, the intracellular ATP concentration fell immediately after transfer to sea water. In contrast, the AMP content increased during the same period, while the ADP content increased slightly. In addition, several morphological changes affected the mitochondria, chromatin and midpiece. These results indicate that the short swimming period of sea bass spermatozoa is controlled by energetic and cytoplasmic ionic conditions and that it is limited by osmotic stress, which induces marked changes in cell morphology. 相似文献
18.
The major components of the internal flagellar apparatus of Chilomonas paramecium Ehr. are two large microtubular roots and a striated root paralleled by three microtubules. The two microtubular roots overlap at the basal bodies. One microtubular root follows a curved path in the anterior of the cell, and the other extends straight to the posterior passing through a groove in the nucleus. The striated root extends laterally from the basal bodies. Except that it is smaller, the posteriorly directed root bears a strong resemblance to the axostyle of oxymonads. The overall arrangement and structure of the flagellar roots is similar to the pelta, axostyle and costa of trichomonads and the pelta and axostyle of oxymonads, groups of mitochondrion-less, largely parasitic or symbiotic protozoans. An affinity between cryptomonads and oxymonads or trichomonads would have many phylogenetic implications, some of which are discussed. 相似文献
19.
Yagi T 《Cell structure and function》2000,25(4):263-267
Previous studies have shown that the motility of flagellar and ciliary axonemes in many organisms are influenced by the concentration of both ATP and ADP. Detergent-extracted cell models of Chlamydomonas oda1, a mutant lacking flagellar outer-arm dynein, displayed slightly lower flagellar beating frequencies when reactivated with ATP in the presence of an ATP-regenerating system, composed of creatine phosphate and creatine phosphokinase, than when reactivated with ATP alone. Thus, presence of a low concentration of ADP may somehow stimulate axonemal motility. To see if this motility stimulation is due to a direct effect on dynein, we analyzed the effect of ADP on the in vitro microtubule translocation caused by isolated inner-arm dyneins in the presence of ATP. Of the seven inner-arm dyneins (species a-g) fractionated by ion-exchange chromatography, most species translocated microtubules at faster speed in the presence of 0.1 mM ATP and 0.1 mM ADP than in the presence of 0.1 mM ATP alone. Most notably, species a and e did not translocate microtubules at all in the presence of the ATP-regenerating system, indicating that a trace amount of ADP is necessary for their motility. This regulation may be effected through binding of ADP to some of the four nucleotide binding sites in each dynein heavy chain. 相似文献
20.
Properties of pyruvate kinase and flagellar ATPase in rabbit spermatozoa: relation to metabolic strategy of the sperm cell 总被引:1,自引:0,他引:1
Rabbit sperm pyruvate kinase remains bound to the cell structure of hypotonically treated mature rabbit epididymal spermatozoa (HTRES). It displays kinetic behavior very similar to that of rabbit muscle pyruvate kinase with regard to KM values for substrates, activation by monovalent and divalent cations, inhibition by phenylalanine which is reversed by alanine, and lack of activation by fructose-1,6-biphosphate. The flagellar ATPase also remains bound to the cell structure of HTRES, whose motility may be reactivated by a source of ATP. It requires Mg+2 for activity; the KM for both ATP and MG+2 is 0.2 mM, implying that MgATP is the substrate. The ATPase activity is not inhibited by ouabain, oligomycin, or vanadate, which also do not affect reconstituted motility, and is not affected by cyclic AMP in the presence of an inhibitor of phosphodiesterase. The activities of pyruvate kinase and the flagellar ATPase in a given preparation of HTRES are comparable. Rabbit spermatozoa have a metabolic strategy which is very similar to muscle cells. This suggests that the major use of the sperm cell's metabolic machinery is maintenance of energy for the contractile work of motility and that only minor amounts of metabolic energy appear to be consumed in other reactions, including those involved in fertilization. 相似文献