Protein Spherulites

Coleman, Joseph E.; Allan, Barbara J.; Vallée, Bert L.

doi:10.1126/science.131.3397.350

Cited by 43 publications

(34 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Cadmium carboxypeptidase hydrolyzes the esters analogous to its natural peptide substrates even more rapidly than the native enzyme (19). Cadmium carbonic anhydrase (HCAB) is active on its ester substrates with a pKaetivity of 9.1 compared to 7.5 to 8 for the native enzyme (20).…”

Section: And Discussionmentioning

confidence: 99%

113Cd NMR as a probe of the active sites of metalloenzymes

Armitage

Uiterkamp

Chlebowski

et al. 1978

Journal of Magnetic Resonance (1969)

View full text Add to dashboard Cite

Section: And Discussionmentioning

confidence: 99%

113Cd NMR as a probe of the active sites of metalloenzymes

Armitage

Uiterkamp

Chlebowski

et al. 1978

Journal of Magnetic Resonance (1969)

View full text Add to dashboard Cite

“…A key to this reactivity is that the zinc sites in metallothionein can undergo associative ligand substitution reactions, so that first-order dissociation rates do not limit the rate of metal transfer. In another comparison, once a metal is bound to carboxypeptidase, it takes many hours of competitive reaction for the more thermodynamically stable metalloprotein to form (19,20). This is presumably because exchange is limited by the dissociation rate of the metal-carboxypeptidase.…”

Section: Discussionmentioning

confidence: 99%

Ligand substitution reactions of metallothioneins with EDTA and apo-carbonic anhydrase.

Li¹,

Kraker²,

Shaw³

et al. 1980

Proc. Natl. Acad. Sci. U.S.A.

187

112

View full text Add to dashboard Cite

The reactions of Zn-, Zn,Cd-, and Cd-thioneins with EDTA and apo-carbonic anhydrase have been studied. The ligand substitution reaction of zinc with EDTA is multiphasic, having both associative and dissociative components in the rate expression. The cadmium sites are about 2 orders of magnitude less reactive. In contrast, apo-carbonic anhydrase abstracts zinc from Zn-thionein and ZnCd-thionein in second-order processes that are 2-3 orders of magnitude more rapid than those involving EDTA and approach the rate for unligated Zn2+ with the apo-protein. In comparison with other zinc proteins, Znthionein contains unusually reactive metal sites, suggesting that this protein may be a physiological zinc transfer protein, able to donate zinc to zinc-requiring apo macromolecules.Although metallothioneins have been known for more than 20 years, insight into their molecular function is only gradually being developed. Metallothionein was discovered as the principal cadmium-binding protein in the cytosol of horse kidney cortex (1). Chemical studies of metallothionein reactions have not progressed far beyond the first report after its identification in cells (2). Hence, although metallothionein binds cadmium after exposure of the host to this toxic metal and recently has been shown to bind zinc and copper under various physiological conditions, no bioinorganic studies have provided a foundation for reasonable hypotheses as to the meaning of these results (3)(4)(5)(6)(7)(8). Such studies are difficult because there are seven sites that may be occupied by a combination of Zn and Cd ions.Recently, we have begun to investigate the metal-sulfhydryl sites of metallothionein to explore possible roles they may play in the metallobiochemistry of cells. Independently, Udom and Brady (9) have published biochemical results consistent with the hypothesis that Zn-thionein may be a physiological donor of zinc to zinc-apometalloproteins. In this communication, data are presented in ligand substitution reactions of various thioneins with EDTA and apo-carbonic anhydrase, which support this thesis. MATERIALSBovine carbonic anhydrase B was purchased from Worthington; 5,5'-dithio-bis(2-nitrobenzoate), phenylmercuric acetate, pnitrophenyl acetate, and pyridine-2,6-dicarboxylic acid were from Sigma; EDTA (gold label) was from Aldrich; 2-carboxy-2'-hydroxy-5'-sulfoformazylbenzene was from Eastman. The metal salts and other chemicals were reagent grade purity. Horse kidney metallothionein was prepared as described (10).Preparation of apo-Carbonic Anhydrase. Bovine carbonic anhydrase B was treated with pyridine-2,6-dicarboxylic acid to remove zinc (11).Analytical Methods. Metal contents of metallothionein and metal-EDTA complexes were measured with a Perkin-Elmer 360 spectrophotometer. The thiol content of metallothionein was measured either colormetrically by using 5,5'-dithiobis(2-nitrobenzoate) or amperometrically by using phenylmercuric acetate as the titrant (12, 13). Disulfide content was determined amperometrically after cleavage of the ...

show abstract

“…In spherulites, the crystallites are suggested to lie along the radius (radial or positive spherulites) or along the circumference (tangential or negative spherulites) (4,6). Several other systems also are known to form spherulites: sodium adducts of DNA (11), proteins such as lysozyme (12,13) and carboxypeptidase (14) under crystallization conditions, tubules from bacteriochlorophyll protein (15), and fibers formed from hemoglobin S, a mutational variant of the human protein leading to sickle cell anemia (16).…”

mentioning

confidence: 99%

The formation of spherulites by amyloid fibrils of bovine insulin

Krebs

MacPhee

Miller

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

236

270

View full text Add to dashboard Cite

Bovine insulin has long been known to self-assemble in vitro into amyloid fibrils. We have observed a further higher-order selfassociation of the protein into spherical structures, with diameters typically around 50 m but ranging from 10 to 150 m. In a polarizing light microscope, these structures exhibit a ''Maltesecross'' extinction pattern typical of spherulites. Spherical structures of a similar size distribution can be observed in the environmental scanning electron microscope, which also reveals the presence of significant amounts of water in the structures. The spherulites contain a large quantity of well defined amyloid fibrils, suggesting that they are formed at least in part as a consequence of the self-assembly of preformed fibrils. Similar structures also have been observed in the tissues of patients suffering from amyloid disorders. The ability of amyloid fibrils to form such higher-order assemblies supports the hypothesis that they represent a generic form of polypeptide structure with properties that are analogous to those of classical synthetic polymers.

show abstract

Protein Spherulites

Cited by 43 publications

References 17 publications

113Cd NMR as a probe of the active sites of metalloenzymes

113Cd NMR as a probe of the active sites of metalloenzymes

Ligand substitution reactions of metallothioneins with EDTA and apo-carbonic anhydrase.

The formation of spherulites by amyloid fibrils of bovine insulin

Contact Info

Product

Resources

About