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PubMed1988

The abundance of calmodulin mRNAs is regulated in phosphorylase kinase-deficient skeletal muscle.

In the I/Lyn mouse strain a mutation on the X chromosome results in a deficiency of the major calmodulin-regulated enzyme in skeletal muscle, phosphorylase kinase. Calmodulin has been identified as the delta-subunit of phosphorylase kinase, and it is estimated that approximately 40% of the total calmodulin in rabbit skeletal muscle is associated with the phosphorylase kinase hexadecamer (alpha, beta, gamma, delta)4. The absence of phosphorylase kinase in I/Lyn skeletal muscle results in a reduction in the total amount of calmodulin. The mechanisms affecting this reduction were investigated by comparing the abundance and heterogeneities in calmodulin mRNAs between normal and phosphorylase kinase-deficient skeletal muscles. The results demonstrate that in normal tissue there are four species of calmodulin mRNA distinguished by their molecular weight. All four of these species are present in the deficient tissue, and none of them are preferentially reduced. However, there is a 54% reduction in all four mRNAs as well as in calmodulin in the deficient skeletal muscle relative to normal skeletal muscle. These results indicate that the expression of calmodulin mRNAs is coordinated with the expression of its major enzyme target in skeletal muscle.

Amino Acid Sequence↗

PubMed1987

Characteristics of calmodulin binding to purified human lymphocyte plasma membranes.

We have explored the role of calmodulin in plasma membrane-related phenomena in lymphocyte activation by measurement of [125I]calmodulin binding to highly purified plasma membrane of human peripheral blood lymphocytes. Calcium-dependent calmodulin binding to lymphocyte membrane was found to reach equilibrium within 5 min of incubation at 37 degrees C and to be saturable and specific. A single class of high affinity-binding sites was identified, with a dissociation constant (Kd) of 1 to 3 X 10(-8) M and a total binding capacity (Bt) of 1 to 2 pmol/mg membrane protein. The free calcium concentration necessary for half-maximal binding was 100 to 300 nM. This was strikingly similar to the cytoplasmic-free calcium activity [Ca2+]i measured by the Quin-2 fluorescence technique, particularly after stimulation with phytomitogens. Calmodulin binding was inhibitable by trifluoperazine (TFP), W-7, and chloropramazine, all of which are calmodulin antagonists. The concentration of TFP that caused 50% inhibition of lymphocyte proliferative responses to phytomitogens was found to be identical to the concentration of TFP which causes 50% inhibition of calmodulin binding to lymphocyte plasma membrane. SDS-polyacrylamide gel electrophoresis followed by gel overlay and autoradiography with iodinated calmodulin revealed five calcium-dependent, TFP-inhibitable, calmodulin-binding polypeptides.

Calcium↗

PubMed1987

Proteolysis of smooth muscle myosin light chain kinase. Formation of inactive and calmodulin-independent fragments.

Proteolysis by trypsin of gizzard myosin light chain kinase in the absence of Ca2+-calmodulin causes a biphasic effect on kinase activity. During the initial phase of proteolysis, Ca2+-calmodulin-dependent kinase activity is reduced over a thousand-fold. Further proteolysis, in the second phase, causes an increase in activity that is independent of Ca2+-calmodulin. Loss of activity is associated with the formation of a 64,000-dalton fragment. Calmodulin-independent activity is associated with the formation of a 61,000-dalton fragment. Procedures for the isolation of each fragment are outlined. Tryptic hydrolysis of the isolated 64,000-dalton peptide generates the 61,000-dalton peptide and increases calmodulin-independent activity. Km values for ATP and light chains for the native kinase and two fragments are the same, i.e. approximately 100 and 5 microM, respectively. Neither fragment binds to F-actin. Amino acid analyses of both fragments are given. Synthetic peptides corresponding to the calmodulin-binding regions of the smooth and skeletal muscle kinases are potent inhibitors of the 61,000-dalton fragment. These data demonstrate the existence of an inhibitory region that is suggested to be located between the active site and the calmodulin-binding site. Whether it is distinct from or at the N-terminal end of the calmodulin-binding site cannot be determined from these data.

Amino Acid Sequence↗

PubMed1985

[The role of free calmodulin in the regulation of calcium-pump activity in erythrocytes].

The activity of Ca-pump in inside-out oriented vesicles obtained from erythrocyte membranes after their 30 min treatment with EGTA at 20 degrees C (membranes A) and 37 degrees C (membranes B) was investigated. It was shown that in membranes A placed into an incubation medium containing 0.1 mM EGTA (pH 7.4) the overall effect of exogenous calmodulin is due to the increase in the maximal activity of the enzyme, its affinity for Ca2+ being unaffected thereby. In membranes B placed into the same medium (pH 6.75) the activation of the Ca-pump by calmodulin is due to the increased affinity for Ca2+ at a constant maximal activity of the enzyme. The dependencies of the value of the calmodulin-stimulated component of membranes A and the Ca2+-binding capacity of calmodulin measured by the intensity of N-phenyl-1-naphthylamine fluorescence on the concentration of free Ca2+ are coincident. In the case of membranes B, the stimulation of Ca-pump by calmodulin occurs at much lower Ca2+ concentrations than the Ca2+ binding-induced conformational shifts in calmodulin. The experimental results suggest that the affinity of the Ca-pump for Ca2+ may affect calmodulin existing in a Ca2+-independent state. The hydrophobic interactions between the Ca-calmodulin complex and the Ca-ATPase molecule are apparently essential for the regulation of the maximal enzyme activity.

Animals↗

PubMed1984

Activation of calmodulin by various metal cations as a function of ionic radius.

The active form of calmodulin is a Ca2+ . calmodulin complex. The purpose of this investigation was to determine whether other metal cations substitute for Ca2+ to activate calmodulin. Binding of Ca2+ resulted in an altered conformation of calmodulin with an increased quantum yield in its tyrosine fluorescence. Qualitatively similar results were obtained with Zn2+, Mn2+, Cd2+, Hg2+, Sr2+, Pb2+, Tb3+, Sm3+, and La3+. The relative extents of fluorescence enhancement by these cations were related to their ionic radii: all cations with ionic radii close to Ca2+ (0.99 A) increased tyrosine fluorescence, whereas those with different ionic radii were not effective, or much less so. The change in calmodulin conformation by the cations was confirmed by its altered electrophoretic mobility on polyacrylamide gels. Cations that change the conformation of calmodulin allow it to stimulate phosphodiesterase. The relative extents of stimulation of phosphodiesterase by cations were also related to their ionic radii. Finally, the ability of metal cations to inhibit Ca2+ binding was similarly related to their ionic radii. In general, the closer the radius of a metal cation was to that of Ca2+, the more effective was the cation to substitute for Ca2+. The range of effective ionic radii was approximately 1 +/- 0.2 A. Calmodulin-stimulated phosphodiesterase activity by the cations was reversed by trifluoperazine, an antagonist of calmodulin.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1982

Effects of acute and chronic morphine treatment of calmodulin activity of rat brain.

The cyclic AMP-phosphodiesterase assay was used to quantitate the amount of calmodulin activity in various brain areas of male rats treated acutely or chronically for 5 days with morphine. The acute treatment with morphine decreased calmodulin activity in the mitochondrial-synaptosomal P2 fraction of the striatum, midbrain, and thalamus but had no effect on the cerebellum, which contains a low density of opiate receptors. The decrease in calmodulin activity by morphine was dose-dependent and was blocked by the opiate antagonist naloxone. In contrast, chronic treatment of rats with morphine increased calmodulin activity in the mitochondrial-synaptosomal P2 of the striatum, midbrain, cerebral cortex, and thalamus. A highly sensitive Ca2+/Mg2+-ATPase assay was also used to quantitate the amount of calmodulin activity in subcellular fractions obtained from the striatum. Chronic morphine treatment caused a significant increase in calmodulin activity in the membrane containing microsomal, synaptosomal, and mitochondrial layers but only a small change in the layer that contained the soluble proteins and the synaptic vesicles. It is suggested that alteration of the content of calmodulin in specific subcellular sites may have a central role in opiate action and addiction via regulation of multiple calmodulin-sensitive biochemical pathways.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1981

Regulation of brain cyclic nucleotide phosphodiesterase by calmodulin. A quantitative analysis.

Comparison of the parameters of Ca and Sr binding to bovine brain calmodulin with the activation of bovine brain phosphodiesterase by Ca2+ and Sr2+ at different calmodulin concentrations allows a quantitative description of the mechanism of activation of the enzyme. Equilibrium dialysis studies show that calmodulin possesses three high affinity (K'diss = 6 micoM) and one low affinity (K'diss = 200 microM) sites for Ca2+. All four sites display the same affinity for Sr2+ with K'diss = 180 microM. In the presence of calmodulin, soluble bovine brain phosphodiesterase is activated by Sr2+ to the same extent as by Ca2+. The activation of the enzyme shows the same Ca2+/Sr2+ selectivity ratio of 30 as the binding of the metal ions to calmodulin. Based on the findings that the Ca2+ or Sr2+ concentration at half-maximal activation of the enzyme depends on the concentration of calmodulin present, a quantitative analysis of activation was carried out as a function of the four calmodulin-metal complex species (CaM . Men). The data show that the activating species are CaM . Ca3, CaM . Ca4 or CaM . Sr3, CaM . Sr4. The interaction of these activating species with phosphodiesterase follows the Hill equation with a dissociation constant of 10(-9) M and a Hill coefficient of 2, irrespective of the binding characteristics of Ca2+ or Sr2+. The latter value agrees well with the fact that phosphodiesterase possesses two binding sites for calmodulin.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1984

Calmodulin-binding proteins in teleost retina, rod inner and outer segments, and rod cytoskeletons.

125I-calmodulin gel overlay techniques have been used to identify calmodulin-binding proteins in teleost retina, in a rod fragment preparation which contains rod inner and outer segments (RIS-ROS), and in RIS-ROS cytoskeletons. We have previously shown that teleost rods change length in response to changes in light conditions, that rod movement is mediated by the actin filaments in the rod inner segment, and that both Ca2+ and cAMP appear to be involved in regulating rod movement. We report here the development of a rod fragment preparation (RIS-ROS), which retains the movable part of the rod, for use in biochemical analysis of rod motility. Gel overlay studies indicate that isolated whole retinas have six prominent calmodulin-binding proteins, migrating at 240 K, 190 K, 150 K, 61 K and a doublet at 18/19 K. In contrast, detached RIS-ROS have three different prominent calmodulin-binding proteins, migrating at 330 K, 33 K, and 31 K. RIS-ROS cytoskeletons have been produced by extraction with Triton X-100; they contain both actin filament bundles and microtubules associated with the connecting cilium. RIS-ROS cytoskeletons have 3 prominent calmodulin-binding proteins migrating at 240 and 18/19 K. These proteins produce faint bands in gel overlays of intact RIS-ROS, but prominent bands in overlays of whole retina. The 240 K protein of RIS-ROS cytoskeletons co-migrates with the 240 K calmodulin-binding subunit of rat brain fodrin. We suggest that the rod 240 K calmodulin-binding protein may be a spectrin-like protein which participates in Ca2+- and calmodulin-regulation of rod motility.

Animals↗

PubMed1984

Calcium-dependent calmodulin binding to cholinergic synaptic vesicles.

Calmodulin is a major nerve terminal protein and a potential mediator of calcium-dependent nerve terminal functions. Calcium-dependent calmodulin binding has been reported in secretory membrane preparations including chromaffin granules and crude rat brain vesicles. Here we demonstrate a calcium-dependent calmodulin-binding site on cholinergic synaptic vesicles from electric organ. It is saturable with high affinity (KD = 10 nM; Bmax = 80 pmol/mg). The binding is inhibited by trifluoperazine (I50 = 8 microM) and is at least 1000-fold specific for calmodulin over troponin C. Association and dissociation rates (k = 3.1 X 10(6) M-1S-1; k-1 = 1.3 X 10(-2) S-1) are consistent with the dissociation constant measured at equilibrium. Intact synaptic vesicles bind to calmodulin immobilized on polyacrylamide matrix, suggesting that the binding site is cytoplasmically oriented in the vesicle population. Intact synaptic vesicles bind calmodulin up to 80-fold more effectively than do side fractions from the vesicle purification. The quantitative difference is largely due to latency of binding sites since it disappears when the binding is assayed in detergent. Binding of calmodulin to proteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis shows that a subset of nerve terminal and electric organ calmodulin-binding proteins are found in synaptic vesicles.

Adenosine Triphosphate↗

PubMed1980

Xenopus laevis oocyte calmodulin in the process of meiotic maturation.

Calcium ions are postulated to be involved in the process of meiotic maturation of amphibian oocytes. Since several of the calcium effects in eukaryotic cells are mediated by calmodulin, the present study was undertaken to assess the presence and level of calmodulin in Xenopus laevis oocytes before and after progesterone treatment. Calmodulin was shown to be present at a concentration of approximately microM in control oocytes cytosol. This level remained stable for 2 h when the maturation promoting factor appeared, and increased to approximately 44 to 59 microM at the time of the germinal vesicle breakdown. Maturation is therefore associated with calmodulin synthesis. Xenopus calmodulin was isolated from oocyte cytosol after heat treatment, anion exchange chromatography, and gel filtration, with a yield of approximately 23%. When compared to mammalian calmodulins, the amphibian protein exhibited the same ultraviolet absorption spectrum, a similar amino acid composition with 1 residue of trimethyllsine, and the same shape conformers in the absence or presence of divalent metals, as shown by different mobilities upon dodecyl sulfate-polyacrylamide gel electrophoresis. The protein migrated faster in the presence than in the absence of Ca2+ ions, Mn2+ and Mg2+ being less effective. It was able to activate calmodulin-deficient myosin light chain kinase. Its high serine content and the tryptic peptide maps obtained after high performance liquid chromatography point, however, to minor differences in the primary structures of mammalian and amphibian calmodulins.

Amino Acids↗

PubMed1994

Molecular interaction between cAMP and calcium in calmodulin-dependent cyclic nucleotide phosphodiesterase system.

The second messenger molecules cAMP and Ca2+ regulate a large number of eukaryotic cellular events. cAMP acts on protein kinases, and Ca2+ works through a ubiquitous calcium-binding protein, calmodulin. The 2 systems are not independent, however, but interact in several important fashions. These interactions can be demonstrated by calmodulin-dependent phosphodiesterase. The bovine heart calmodulin-dependent phosphodiesterase can be phosphorylated by cAMP-dependent protein kinase, resulting in a decrease in the enzyme's affinity for calmodulin. The phosphorylation of calmodulin-dependent phosphodiesterase is blocked by Ca2+ and calmodulin, and reversed by the calmodulin-dependent phosphatase (calcineurin). The dephosphorylation is accompanied by an increase in the affinity of the phosphodiesterase for calmodulin. Results from this study suggest that the activity of this phosphodiesterase is precisely regulated by cross-talk between Ca2+ and cAMP signalling pathways.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1996

Effect of calmodulin antagonists on endocytosis and intracellular transport of ricin in polarized MDCK cells.

The effect of calmodulin antagonists on endocytosis, transcytosis, recycling, and transport to the Golgi apparatus from both the apical and the basolateral plasma membrane of polarized Madin-Darby canine kidney cells has been investigated by using the plant toxin ricin as a membrane marker. The calmodulin antagonists trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) stimulated apical endocytosis of ricin, whereas basolateral endocytosis was unaffected. A stimulation of the apical uptake of the fluid-phase marker horseradish peroxidase by calmodulin antagonists was also found both by biochemical and by ultrastructural studies. Furthermore, W-7 reduced the recycling of ricin to the apical plasma membrane, whereas the recycling to the basolateral plasma membrane was not changed. Transport of ricin to the Golgi apparatus was also selectively affected by the calmodulin antagonist W-7. After basolateral endocytosis of ricin, transport to the Golgi apparatus was reduced, whereas after apical endocytosis the fraction of endocytosed ricin transport to the Golgi apparatus was increased. Transcytosis of ricin from the basolateral to the apical pole was increased in the presence of calmodulin antagonists, whereas these compounds did not have any significant effect on the apical to basolateral transcytosis. Thus, the results obtained indicate that calmodulin is involved in regulation of apical endocytosis and recycling as well as in transcytosis of ricin from the basolateral plasma membrane. Furthermore, the data suggest that calmodulin plays a role in regulation of ricin transport to the Golgi apparatus.

Animals↗

PubMedDate not supplied

Models of calmodulin trapping and CaM kinase II activation in a dendritic spine.

Activation of calcium/calmodulin-dependent protein kinase II (CaMKII) by calmodulin following calcium entry into the cell is important for long-term potentiation (LTP). Here a model of calmodulin binding and trapping by CaMKII in a dendritic spine was used to estimate levels and durations of CaMKII activation following LTP-inducing tetani. The calcium signal was calcium influx through NMDA receptor channels computed in a highly detailed dentate granule cell model. Calcium could bind to calmodulin and calmodulin to CaMKII. CaMKII subunits were either free, bound with calmodulin, trapped, autonomous, or capped. Strong low-frequency tetanic input produced little calmodulin trapping or CaMKII activation. Strong high-frequency tetanic input caused large numbers of CaMKII subunits to become trapped, and CaMKII was strongly activated. Calmodulin trapping and CaMKII activation were highly dependent on tetanus frequency (particularly between 10 and 100 Hz) and were highly sensitive to relatively small changes in the calcium signal. Repetition of a short high-frequency tetanus was necessary to achieve high levels of CaMKII activation. Three stages of CaMKII activation were found in the model: a short, highly activated stage; an intermediate, moderately active stage; and a long-lasting third stage, whose duration depended on dephosphorylation rates but whose decay rate was faster at low CaMKII activation levels than at high levels. It is not clear which of these three stages is most important for LTP.

Action Potentials↗

PubMed1987

Effects of isoproterenol on active force and Ca2+ X calmodulin-sensitive phosphodiesterase activity in porcine coronary artery.

Relaxation of vascular smooth muscle following beta-adrenergic stimulation may result from reduction of the cytoplasmic Ca2+ concentration, reduction in the sensitivity of the contractile apparatus to Ca2+, or both. To help resolve these possibilities, we measured the extent of activation of Ca2+ X calmodulin-sensitive phosphodiesterase in intact porcine coronary artery strips as a functional indicator of the cytoplasmic Ca2+ concentration. Both calmodulin-stimulated phosphodiesterase activity and active force increased during K+ stimulation of coronary artery strips. Relaxation of K+-contracted artery strips following stimulus withdrawal was accompanied by rapid inactivation of Ca2+ X calmodulin-sensitive phosphodiesterase. The temporal relationship between isoproterenol-induced relaxation and inactivation of Ca2+ X calmodulin-sensitive phosphodiesterase was studied in both histamine- and K+-contracted tissues. Stimulation of strips with 10 microM histamine or with 44 mM K+ led to comparable increases both in active force and in calmodulin-stimulated phosphodiesterase activity. Thereafter, sustained contraction elicited by histamine was accompanied by a decrease in calmodulin-stimulated phosphodiesterase activity. Isoproterenol rapidly relaxed histamine-contracted strips and accelerated the decrease in phosphodiesterase activity. In contrast, sustained contraction in response to K+ was accompanied by a sustained elevation of calmodulin-stimulated phosphodiesterase activity. Isoproterenol treatment of K+-contracted tissues led to relaxation that was slow and incomplete, and it had very little effect on calmodulin-stimulated phosphodiesterase activity. We conclude that reduction of the cytoplasmic Ca2+ concentration is important for rapid relaxation of the coronary artery following beta-adrenergic stimulation. We cannot disallow the possibility that a decrease in the sensitivity of the contractile apparatus to Ca2+ is involved to some degree.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1996

Modulation of an Intracellular Calmodulin-Stimulated Ca2+-Pumping ATPase in Cauliflower by Trypsin (The Use of Calcium Green-5N to Measure Ca2+ Transport in Membrane Vesicles).

The effect of controlled trypsin digestion of a calmodulin-stimulated Ca2+-ATPase in low-density intracellular membranes from cauliflower (Brassica oleracea L.) inflorescences was investigated. Ca2+ uptake into vesicles was measured either continuously with the fluorescent Ca2+ indicator Calcium Green-5N or with a radio-active filter technique. Trypsin treatment of vesicles resulted in a 3-fold activation of Ca2+ uptake and loss of calmodulin sensitivity. Immunoblotting experiments with an antiserum raised against the Ca2+-ATPase showed that the trypsin activation was accompanied by a decrease in the amount of intact Ca2+-ATPase (111 kD) and by successive appearances of polypeptides of 102 and 99 to 84 kD. 125I-Calmodulin overlays showed that only the intact Ca2+-ATPase bound calmodulin. Removal of the calmodulin-binding domain (about 9 kD) was not enough to obtain full activation. Trypsin proteolysis resulted in a Ca2+ concentration necessary for half-maximal activity of 0.5 [mu]M, whereas a value of about 2 [mu]M was obtained with untreated membranes in the presence of calmodulin. Without trypsin treatment or calmodulin the activity was not saturated even at 57 [mu]M free Ca2+. The data suggest that trypsin digestion and calmodulin activate the cauliflower Ca2+-ATPase by at least partly different mechanisms.

Journal Article↗

PubMed1992

Plasma Membrane Ca-ATPase of Radish Seedlings : II. Regulation by Calmodulin.

The effect of calmodulin on the activity of the plasma membrane Ca-ATPase was investigated on plasma membranes purified from radish (Raphanus sativus L.) seedlings. Calmodulin stimulated the hydrolytic activity and the transport activity of the plasma membrane Ca-ATPase to comparable extents in a manner dependent on the free Ca(2+) concentration. Stimulation was marked at low, nonsaturating Ca(2+) concentrations and decreased increasing Ca(2+), so that the effect of calmodulin resulted in an increase of the apparent affinity of the enzyme for free Ca(2+). The pattern of calmodulin stimulation of the plasma membrane Ca-ATPase activity was substantially the same at pH 6.9 and 7.5, in the presence of ATP or ITP, and when calmodulin from radish seeds was used rather than that from bovine brain. At pH 6.9 in the presence of 5 micromolar free Ca(2+), stimulation of the plasma membrane Ca-ATPase was saturated by 30 to 50 micrograms per milliliter bovine brain calmodulin. The calmodulin antagonist calmidazolium inhibited both basal and calmodulin-stimulated plasma membrane Ca-ATPase activity to comparable extents.

Journal Article↗

PubMed1985

The design, synthesis, and characterization of tight-binding inhibitors of calmodulin.

Based on a consideration of the probable structure of calmodulin and some natural peptides known to interact with it, two calmodulin-binding peptides were designed. These peptides bind to calmodulin in helical conformations and are capable of forming electrostatic and hydrophobic interactions with calmodulin. Their dissociation constants for binding (less than or equal to 210 and 400 pM) place them as the tightest-binding inhibitors of calmodulin thus far reported. The study of the interactions of these and similar peptides with calmodulin will provide valuable insights into the mechanisms whereby calmodulin binds to target enzymes, and it also serves as an excellent model system for exploring the physical chemistry of protein-protein interaction.

Amino Acid Sequence↗

PubMed1995

Fluorescence of a tryptophan bearing peptide from smooth muscle myosin light chain kinase upon binding to two closely related calmodulins.

We have investigated the fluorescence of a calmodulin binding peptide (AS19) based on the sequence of the calmodulin binding domain of smooth muscle myosin light chain kinase and bearing a tryptophan residue at position 5 upon binding to two closely related calmodulins. The emission maximum of peptide AS19 bound to the engineered SYNCAM calmodulin was 318 nm and a vibrational structure was clearly apparent. The emission maximum of peptide AS19 bound to chicken gizzard calmodulin (ChG CaM) was 327 nm and its spectrum was featureless. Red edge excitation effect supports the assumption that the polarity of Trp-5 environment is larger in the complex with ChG CaM than with SYNCAM, in agreement with fluorescence spectra. Time-resolved fluorescence and anisotropy measurements showed that, in both complexes, the tryptophan emitting state was 1La. The X-ray structure of the calmodulin-peptide complex has been resolved (W. E. Meador, A. R. Means, and F. A. Quiocho, 1992, Science 257, 1251-1255). The Trp binding site has been characterized. It differs by a single-point mutation between the two calmodulins: Met-144 of ChG CaM has been replaced by Val in SYNCAM. This suggests that the spectral relaxation of Trp-5 in the complex with ChG CaM as compared to SYNCAM is due to the polarizability of the sulfur atom containing Met side chain that is higher than that of Val. This provides an ideal system to investigate the origin of the Stokes shift of the indole moiety in proteins.

Amino Acid Sequence↗