Biomedical subjects

J A Greenwood

Publications and source records attributed to J A Greenwood.

At least 19 recordsLinked to original sources

PubMed2005

Oscillatory loading of a viscoelastic adhesive contact.

The cycle of loading and unloading of a spherically-tipped probe against an adhesive, viscoelastic plane specimen is studied by numerical integration of the relations between crack speed and apparent surface energy previously found for a linear 3-element viscoelastic solid with a Maugis-Dugdale law of force across the crack. It is found that even when the rate of loading is so slow that the loading and unloading curves almost coincide, suggesting purely elastic behaviour, the pull-off force can be appreciably greater than the elastic (JKR) value. When the normal force is modulated with a small amplitude sinusoidal variation during unloading--in order to find the contact stiffness--the contact radius barely changes, and the stiffness is close to that for a rigid flat punch instead of having the expected JKR value.

Journal Article↗

PubMed2005

Oscillating adhesive contacts between micron-scale tips and compliant polymers.

Adhesion of micron-scale probes with model poly(dimethylsiloxane), PDMS, elastomers was studied with a depth-sensing nanoindenter under oscillatory loading conditions. For contacts between diamond indenters (radius R = 5 or 10 microm) and PDMS, force-displacement curves were highly reversible and consistent with Johnson-Kendall-Roberts (JKR) behavior. However, our experiments have revealed striking differences between the experimental measurements of tip-sample interaction stiffness and the theoretical JKR stiffness. The measured stiffness was always greater than zero, even in the reflex portion of the curve (between the maximum adhesive force and release), where the JKR stiffness is negative. This apparent paradox can be resolved by considering the effects of viscoelasticity of PDMS on an oscillating crack tip in a JKR contact. Under well described conditions determined by oscillation frequency, sample viscoelastic properties, and the Tabor parameter (with variables R, reduced elastic modulus, E*, and interfacial energy, deltagamma), an oscillating crack tip will neither advance nor recede. In that case, the contact size is fixed (like that of a flat punch) at any given point on the load-displacement cycle, and the experimentally measured stiffness is equal to the equivalent punch stiffness. For a fixed oscillation frequency, a transition between JKR and punch stiffness can be brought about by an increase in radius of the probe or a decrease in PDMS modulus. Additionally, varying the oscillation frequency for a fixed E*, R, and deltagamma also resulted in transition between JKR and punch stiffness in a predictable manner. Comparisons of experiments and theory for an oscillating viscoelastic JKR contact are presented. The storage modulus and surface energy from nanoscale JKR stiffness measurements were compared to calculated values and those measured with conventional nanoindentation and JKR force-displacement analyses.

Journal Article↗

PubMed2005

The buckling of spherical liposomes.

In the classical "first approximation" theory of thin-shell structures, the constitutive relations for a generic shell element--i.e. the elastic relations between the bending moments and membrane stresses and the corresponding changes in curvature and strain, respectively-are written as if an element of the shell is flat, although in reality it is curved. In this theory it is believed that discrepancies on account of the use of "flat" constitutive relations will be negligible provided the ratio shell-radius/thickness is of sufficiently large order. In the study of drawing of narrow, cylindrical "tethers" from liposomes it has been known for many years that it is necessary to use instead a constitutive law which explicitly describes a curved element in order to make sense of the mechanics; and indeed such tethers are generally of "thick-walled" proportions. In this paper we show that the proper constitutive relations for a curved element must also be used in the study, by means of shell equations, of the buckling of initially spherical thin-walled giant liposomes under exterior pressure: these involve the inclusion of what we call the "Mkappa" terms, which are not present in the standard "first-approximation" theory. We obtain analytical expressions for both the bifurcation buckling pressure and the slope of the post-buckling path, in terms of the dimensions and elastic constants of the lipid bi-layer, and also the initial state of bending moment in the vesicle. We explain physically how the initial bending moment can affect the bifurcation pressure, whereas it cannot in "first-approximation" theory. We use these results to map the conditions under which the vesicle buckles into an oblate, as distinct from a prolate ("rugby-ball") shape. Some of our results were obtained long ago by the use of energy methods; but our aim here has been to identify precisely what is lacking in "first-approximation" theory in relation to liposomes, and so to put the "shell equations" approach onto a firm footing in mechanics.

Computer Simulation↗

PubMed2002

Mechanics of tether formation in liposomes.

It is well-known that a "tether" may be drawn out from a pressurized liposome by means of a suitably applied radial-outward force applied locally to the lipid bilayer. The tether is a narrow, uniform cylindrical tube, which joins the main vesicle in a short "transition region." A first-order energy analysis establishes the broad relationship between the force F needed to draw the tether, the radius R0 of the tether, the bending-stiffness constant B for the lipid bilayer and the membrane tension T in the pressurized liposome. The aim of the present paper is to study in detail the "transition region" between the tether and the main vesicle, by means of a careful application of the engineering theory of axisymmetric shell structures. It turns out that the well-known textbook "thin-shell" theory is inadequate for this purpose, because the tether is evidently an example of a thick-walled shell; and a novel ingredient of the present study is the introduction of elastic constitutive relations that are appropriate to the thick-shell situation. The governing equations are set up in dimensionless form, and are solved by means of a "shooting" technique, starting with a single disposable parameter at a point on the meridian in the tether, which can be adjusted until the boundary conditions at the far "equator" of the main vessel are satisfied. It turns out that the "transition region" between the tether and the main vessel is well characterized by only a few parameters, while the tether and main vessel themselves are described by very simple equations. Introduction of the thick-shell constitutive relation makes little difference to the conformation of and stress-resultants in, the main vessel; but it makes a great deal of difference in the tether itself Indeed, a kind of phase-change appears to take place in the "transition region" between these two zones of the liposome.

Computer Simulation↗

PubMed2000

Restructuring of focal adhesion plaques by PI 3-kinase. Regulation by PtdIns (3,4,5)-p(3) binding to alpha-actinin.

Focal adhesions are an elaborate network of interconnecting proteins linking actin stress fibers to the extracellular matrix substrate. Modulation of the focal adhesion plaque provides a mechanism for the regulation of cellular adhesive strength. Using interference reflection microscopy, we found that activation of phosphoinositide 3-kinase (PI 3-kinase) by PDGF induces the dissipation of focal adhesions. Loss of this close apposition between the cell membrane and the extracellular matrix coincided with a redistribution of alpha-actinin and vinculin from the focal adhesion complex to the Triton X-100-soluble fraction. In contrast, talin and paxillin remained localized to focal adhesions, suggesting that activation of PI 3-kinase induced a restructuring of the plaque rather than complete dispersion. Furthermore, phosphatidylinositol (3,4, 5)-trisphosphate (PtdIns (3,4,5)-P(3)), a lipid product of PI 3-kinase, was sufficient to induce restructuring of the focal adhesion plaque. We also found that PtdIns (3,4,5)-P(3) binds to alpha-actinin in PDGF-treated cells. Further evidence demonstrated that activation of PI 3-kinase by PDGF induced a decrease in the association of alpha-actinin with the integrin beta subunit, and that PtdIns (3,4,5)-P(3) could disrupt this interaction in vitro. Modification of focal adhesion structure by PI 3-kinase and its lipid product, PtdIns (3,4,5)-P(3), has important implications for the regulation of cellular adhesive strength and motility.

Actinin↗

PubMed1998

Signaling of de-adhesion in cellular regulation and motility.

Adhesion is a process that can be divided into three separate stages: (1) cell attachment, (2) cell spreading, and (3) the formation of focal adhesions and stress fibers. With each stage the adhesive strength of the cell increases. De-adhesion can be defined as the process involving the transition of the cell from a strongly adherent state, characterized by focal adhesions and stress fibers, to a state of intermediate adherence, represented by a cell that is spread, but that lacks stress fibers terminating at adhesion plaques. We propose that this modification of the structural link between the actin cytoskeleton and the extracellular matrix results in a more malleable cellular state conducive for dynamic processes such as cytokinesis, mitogenesis, and motility. Anti-adhesive proteins, including thrombospondin, tenascin, and SPARC, rapidly signal de-adhesion, potentially mediating proliferation and migration during development and wound healing. Intracellular signaling molecules involved in the regulation of de-adhesion are only beginning to be identified. Interestingly, many of the same signaling proteins recognized to play important roles during the process of adhesion have also been found to act during de-adhesion. Characterization of the precise mechanisms by which these signals modulate adhesive structures and the cytoskeleton will further our understanding of the regulation of adhesive strength and its function in cellular physiology.

Actin Cytoskeleton↗

PubMed1998

Thrombospondin signaling of focal adhesion disassembly requires activation of phosphoinositide 3-kinase.

Thrombospondin is an extracellular matrix protein involved in modulating cell adhesion. Thrombospondin stimulates a rapid loss of focal adhesion plaques and reorganization of the actin cytoskeleton in cultured bovine aortic endothelial cells. The focal adhesion labilizing activity of thrombospondin is localized to the amino-terminal domain, specifically amino acids 17-35. Use of a synthetic peptide (hep I), containing amino acids 17-35 of thrombospondin, enables us to examine the signaling mechanisms specifically involved in thrombospondin-induced disassembly of focal adhesions. We tested the hypothesis that activation of phosphoinositide 3-kinase is a necessary step in the thrombospondin-induced signaling pathway regulating focal adhesion disassembly. Both wortmannin and LY294002, membrane permeable inhibitors of phosphoinositide 3-kinase activity, blocked hep I-induced disassembly of focal adhesions. Similarly, wortmannin inhibited hep I-mediated actin microfilament reorganization and the hep I-induced translocation of alpha-actinin from focal adhesion plaques. Hep I also stimulated phosphoinositide 3-kinase activity approximately 2-3-fold as measured in anti-phosphoinositide 3-kinase and anti-phosphotyrosine immunoprecipitates. Increased immunoreactivity for the 85-kDa regulatory subunit in anti-phosphotyrosine immunoprecipitates suggests that the p85/p110 form of phosphoinositide 3-kinase is involved in this pathway. In 32Pi-labeled cells, hep I increased levels of phosphatidylinositol (3,4,5)-trisphosphate, the major product of phosphoinositide 3-kinase phosphorylation. These results suggest that thrombospondin signals the disassembly of focal adhesions and reorganization of the actin cytoskeleton by a pathway involving stimulation of phosphoinositide 3-kinase activity.

Amino Acid Sequence↗

PubMed1998

Characterisation of a binding-protein-dependent, active transport system for short-chain amides and urea in the methylotrophic bacterium Methylophilus methylotrophus.

Three genes (fmdCAB) encoding an outer-membrane porin for short-chain amides and urea, formamidase, and a putative regulatory protein in Methylophilus methylotrophus have previously been cloned and characterised. Three genes have now been identified downstream of fmdB, viz fmdD encoding a hydrophilic protein containing an N-terminal signal sequence, and fmdEF encoding hydrophobic transmembrane proteins. The derived amino acid sequence of mature FmdD (predicted molecular mass 41,870 Da) was similar to the cytoplasmic, amide-binding protein (AmiC) from Pseudomonas aeruginosa and to several periplasmic, solute-binding proteins from other bacteria. Mature FmdD was purified and shown to be a monomer (40-45 kDa) with the predicted N-terminal amino acid sequence (ADYPTA-). Equilibrium dialysis showed that the purified protein bound short-chain amides and urea with high affinity (Kd 7.2 microM for [14C]urea). SDS/PAGE and western blotting using antiserum to mature FmdD showed it was induced by short-chain amides and urea, and repressed by excess ammonia. The derived amino acid sequences of FmdE (32,822 Da) and FmdF (incomplete; >25,435 Da) were similar to the transmembrane proteins BraD/LivH and BraE/LivM, respectively, in various leucine/isoleucine/valine transport systems. Uptake of [14C]urea by washed cells was inhibited by the uncoupling agent carbonyl cyanide p-trifluoromethoxyphenylhydrazone and unlabelled formamide. It is concluded that FmdDEF comprise part of a high-affinity, binding-protein-dependent active-transport system for short-chain amides and urea in M. methylotrophus.

Amides↗

PubMed1996

Cyclic GMP-dependent protein kinase is required for thrombospondin and tenascin mediated focal adhesion disassembly.

Focal adhesions are specialized regions of cell membranes that are foci for the transmission of signals between the outside and the inside of the cell. Intracellular signaling events are important in the organization and stability of these structures. In previous work, we showed that the counter-adhesive extracellular matrix proteins, thrombospondin, tenascin, and SPARC, induce the disassembly of focal adhesion plaques and we identified the active regions of these proteins. In order to determine the mechanisms whereby the anti-adhesive matrix proteins modulate cytoskeletal organization and focal adhesion integrity, we examined the role of protein kinases in mediating the loss of focal adhesions by these proteins. Data from these studies show that cGMP-dependent protein kinase is necessary to mediate focal adhesion disassembly triggered by either thrombospondin or tenascin, but not by SPARC. In experiments using various protein kinase inhibitors, we observed that selective inhibitors of cyclic GMP-dependent protein kinase, KT5823 and Rp-8-Br-cGMPS, blocked the effects of both the active sequence of thrombospondin 1 (hep I) and the alternatively-spliced segment (TNfnA-D) of tenascin-C on focal adhesion disassembly. Moreover, early passage rat aortic smooth muscle cells which have high levels of cGMP-dependent protein kinase were sensitive to hep I treatment, in contrast to passaged cGMP-dependent protein kinase deficient cells which were refractory to hep I or TNfnA-D treatment, but were sensitive to SPARC. Transfection of passaged smooth muscle cells with the catalytic domain of PKG I alpha restored responsiveness to hep I and TNfnA-D. While these studies show that cGMP-dependent protein kinase activity is necessary for thrombospondin and tenascin-mediated focal adhesion disassembly, kinase activity alone is not sufficient to induce disassembly as transfection of the catalytic domain of the kinase in the absence of additional stimuli does not result in loss of focal adhesions.

Animals↗

PubMed1995

Localization and in situ phosphorylation state of nuclear tau.

The localization and phosphorylation state of tau in LA-N-5 neuroblastoma cells was examined. Our results demonstrate that there are two populations of tau in LA-N-5 cells: cytosolic tau and nuclear tau. Indirect immunofluorescent microscopy revealed that nuclear tau is specifically localized to the nucleolus while cytosolic tau is diffusely distributed. To localize and quantitate tau in LA-N-5 cells by subcellular fractionation, a method was developed to extract tau from the nucleus while preserving the endogenous state of the protein. These studies revealed that 16% of the total tau protein in LA-N-5 cells is located in the nucleus and more specifically was found predominantly in the chromatin fraction containing DNA, chromatin, and associated proteins. The phosphorylation state of nuclear and cytosolic tau was examined by labeling LA-N-5 cells with 32Pi and immunoprecipitating tau from the different fractions. These data demonstrated that nuclear tau and cytosolic tau are phosphorylated approximately to the same extent. To determine if the phosphorylation of nuclear tau occurs in the nucleus, LA-N-5 nuclei were isolated, incubated with [gamma-32P]ATP, extracted, and tau was immunoprecipitated. Although numerous nuclear proteins were 32P-labeled, tau was not phosphorylated. These results suggest that nuclear tau is not phosphorylated in the nucleus but rather in the cytosol prior to transport into the nucleus. The specific localization of nuclear tau strongly suggests that it has a functional role in the nucleus. However, further studies are necessary to determine the function of nuclear tau and how it may be regulated by phosphorylation.

Autoradiography↗

PubMed1995

Agrobacterium radiobacter and related organisms take up fructose via a binding-protein-dependent active-transport system.

Washed cells of Agrobacterium radiobacter prepared from a fructose-limited continuous culture (D 0.045 h-1) transported D(-)[U-14C]fructose in a linear manner for up to 4 min at a rate several-fold higher than the rate of fructose utilization by the growing culture. D(-)[U-14C]Fructose transport exhibited a high affinity for fructose (KT < 1 microM) and was inhibited to varying extents by osmotic shock, by the uncoupling agent carbonyl cyanide p-trifluoromethoxyphenylhydrazone, and by unlabelled sugars (D-fructose/D-mannose > D-ribose > D-sorbose > D-glucose/D-galactose/D-xylose; no inhibition by D-arabinose). Prolonged growth of A. radiobacter in fructose-limited continuous culture led to the selection of a novel strain (AR100) which overproduced a fructose-binding protein (FBP) and showed an increased rate of fructose transport. FBP was purified from osmotic-shock fluid using anion-exchange fast protein liquid chromatography (FPLC). The monomeric protein (M(r) 34,200 by SDS-PAGE and 37,700 by gel-filtration FPLC) bound D-[U-14C]-fructose stoichiometrically (1.17 nmol nmol FBP-1) and with high affinity (KD 0.49 microM) as shown by equilibrium dialysis. Binding of D-[U-14C]fructose by FBP was variably inhibited by unlabelled sugars (D-fructose/D-mannose > D-ribose > D-sorbose; no inhibition by D-glucose, D-galactose or D-arabinose). The N-terminal amino acid sequence of FBP (ADTSVCLI-) was similar to that of several sugar-binding proteins from other species of bacteria. Fructose transport and FBP were variably induced in batch cultures of A. radiobacter by growth on different carbon sources (D-fructose > D-ribose/D-mannose > D-glucose; no induction by succinate). An immunologically similar protein to FBP was produced by Agrobacterium tumefaciens and various species of Rhizobium following growth on fructose. It is concluded that fructose is transported into A. radiobacter and related organisms via a periplasmic fructose/mannose-binding-protein-dependent active-transport system, in contrast to the phosphotransferase system used by many other species of bacteria.

Amino Acid Sequence↗

PubMed1994

Casein kinase II preferentially phosphorylates human tau isoforms containing an amino-terminal insert. Identification of threonine 39 as the primary phosphate acceptor.

The in vitro phosphorylation of the microtubule-associated protein tau by casein kinase II was studied. Purified human brain tau was phosphorylated by casein kinase II to a stoichiometry of 0.7 mol of 32P/mol of tau. Individual recombinant human tau isoforms were phosphorylated to stoichiometries ranging from 0.2 to 0.8 mol of 32P/mol of tau. Casein kinase II catalyzed a 4-fold greater incorporation of phosphate into the tau isoform containing a 58-amino acid insert near its amino terminus (T4L) than the isoforms without the 58-amino acid insert (T3 and T4). Phosphopeptide mapping of casein kinase II phosphorylated human tau and recombinant tau isoforms suggested that the isoforms containing an amino-terminal insert constitute the major substrates for casein kinase II within the tau family. The sites of phosphorylation on T4L were identified by digesting phosphorylated T4L with the protease Asp-N, separating the peptides by reversed phase high performance liquid chromatography, and analyzing the isolated peptides by liquid-secondary ion mass spectrometry and solid-phase amino-terminal sequencing. Thr39 was identified as the predominant phosphorylation site, which is located 5 residues from the amino-terminal insert in T4L. Phosphopeptide mapping of tau isolated from LA-N-5 neuroblastoma cells indicates that Thr39 is phosphorylated in situ. To our knowledge, this is the first demonstration of a differential phosphorylation of the human tau isoforms, with the isoforms containing the acidic amino-terminal insert being the preferred substrates of casein kinase II.

Amino Acid Sequence↗

PubMed1994

The effect of nutrient limitation on glycerol uptake and metabolism in continuous cultures of Pseudomonas aeruginosa.

Pseudomonas aeruginosa NM48, a non-mucoid derivative of an alginate-producing strain isolated from a cystic fibrosis patient, was grown in batch culture with glycerol, glucose or succinate as carbon source, and in continuous culture (D 0.05 h-1) under glycerol or glucose limitation. Glycerol uptake, glycerol kinase and glycerol-3-phosphate dehydrogenase were induced by glycerol, but not by glucose or succinate. Linear uptake of [14C]glycerol by washed cells (Km < or = 2 microM) was inhibited by unlabelled glycerol and glyceraldehyde, but not by cyanide or the uncoupling agent carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), and was accompanied by substantial intracellular accumulation of glycerol-3-phosphate and/or dihydroxyacetone phosphate but not glycerol. Prolonged growth under glycerol limitation led to substantial increases in the activities and/or concentrations of the enzymes catalysing glycerol uptake and metabolism, together with a 48,000 M(r) outer-membrane protein which was also over-expressed following prolonged growth under glucose limitation. The N-terminal amino acid sequence (AEAFSPN-) and electrophoretic properties of this protein were the same as those of the previously characterized glucose porin (OprB) from P. aeruginosa, indicating that this porin is active with both glucose and glycerol. It is concluded that during growth under glycerol limitation, glycerol is transported into P. aeruginosa NM48 via OprB and a high-affinity, binding-protein-independent facilitated-diffusion system.

Adaptation, Biological↗

PubMed1993

Phosphorylation modulates calpain-mediated proteolysis and calmodulin binding of the 200-kDa and 160-kDa neurofilament proteins.

The effects of enzymatic dephosphorylation on neurofilament interaction with two calcium-binding proteins, calpain and calmodulin, were examined. Dephosphorylation increased the rate and extent of 200-kDa neurofilament protein proteolysis by calpain. In contrast, dephosphorylation of the 160-kDa neurofilament protein did not alter the rate or extent of calpain proteolysis. However, the calpain-induced breakdown products of native and dephosphorylated 160-kDa neurofilament protein were different. Dephosphorylation did not change the proteolytic rate, extent, or breakdown products of the 68-kDa neurofilament protein. Calmodulin binding to the purified individual 160- and 200-kDa neurofilament proteins was increased following dephosphorylation. These results suggest that phosphorylation may regulate the metabolism and function of neurofilaments by modulating interactions with the calcium-activated proteins calpain and calmodulin.

Animals↗

PubMed1992

Brain casein kinase 2: affinity purification procedure using immobilized polyethylenimine.

A simplified procedure for casein kinase 2 purification from bovine brain is described. The purification procedure consists of two affinity chromatography steps, using heparin and polyethylenimine immobilized on a synthetic matrix (Toyopearl 650M). The adsorption and elution conditions for each column were optimized, resulting in a simple elution protocol for each column. A stable, highly purified casein kinase 2 preparation was obtained in 4 h using this procedure. Polyethylenimine was shown to stimulate the casein kinase 2 activity using exogeneous substrates (casein, calmodulin, MAP2, and tau) but not the enzyme's autophosphorylation activity. The polyethylenimine stimulation could be overcome by applying a mass excess of the casein kinase 2 inhibitor, heparin.

Animals↗

PubMed1992

Molecular analysis of the lac operon encoding the binding-protein-dependent lactose transport system and beta-galactosidase in Agrobacterium radiobacter.

The genes coding for the binding-protein-dependent lactose transport system and beta-galactosidase in Agrobacterium radiobacter strain AR50 were cloned and partially sequenced. A novel lac operon was identified which contains genes coding for a lactose-binding protein (lacE), two integral membrane proteins (lacF and lacG), an ATP-binding protein (lacK) and beta-galactosidase (lacZ). The operon is transcribed in the order lacEFGZK. The operon is controlled by an upstream regulatory region containing putative -35 and -10 promoter sites, an operator site, a CRP-binding site probably mediating catabolite repression by glucose and galactose, and a regulatory gene (lacl) encoding a repressor protein which mediates induction by lactose and other galactosides in wild-type A. radiobacter (but not in strain AR50, thus allowing constitutive expression of the lac operon). The derived amino acid sequences of the gene products indicate marked similarities with other binding-protein-dependent transport systems in bacteria.

Amino Acid Sequence↗

PubMed1992

Estrogen control of uterine tissue factor messenger ribonucleic acid levels.

One of the early responses of the immature rat uterus to stimulation by estradiol (E2) is an increase in the specific activity and synthesis of a discrete set of proteins including tissue factor (TF). Increases in TF are associated with stimulation of cell growth in mouse and human fibroblasts and endothelial cells. The increase in TF activity following E2 stimulation of the uterus is due to an increase in TF messenger RNA (mRNA). A 2- to 4-fold increase in mRNA is observed 1 h after injection, reaches a maximum at 3 h, and is reduced at 6 h. The increase is hormone specific and occurs at low levels of E2 (0.66 micrograms/kg). The E2 effect is abolished by actinomycin but not by cycloheximide. The changes in TF mRNA occur in a similar time scale and at similar E2 doses as the increases in the uterine proto-oncogenes c-jun and c-fos.

Animals↗

PubMed1991

The regulatory role of calmodulin in the proteolysis of individual neurofilament proteins by calpain.

The in vitro degradation of individual neurofilament proteins by calpain and the effects of calmodulin on this proteolysis were studied. Two major results are reported. First, in the presence of calcium, calmodulin binds to the 200-kD neurofilament protein, but only weakly associates with the 150-kD neurofilament protein. The 70-kD neurofilament protein shows no specific calmodulin-binding. Second, calmodulin inhibits the calpain-mediated degradation of the 200-kD neurofilament protein, but does not alter the hydrolysis of the 150-kD and 70-kD neurofilament proteins. In addition, calmodulin is able to bind to the 200-kD neurofilament protein in the presence of other neurofilament subunits, indicating that calmodulin may play a role in the regulation of the metabolism of the 200-kD neurofilament protein in vivo.

Animals↗