Inorganic Biochemistry Volume 2

A Review of the Recent Literature Published Up to Mid 1979

By H. A. O. Hill

The Royal Society of Chemistry

Copyright © 1981 The Royal Society of Chemistry
All rights reserved.
ISBN: 978-0-85186-555-3

Contents

Chapter 1 Inorganic Analogues of Biological Molecules By C. A. McAuliffe, 1,
Chapter 2 Storage, Transport, and Function of Non-transition Elements By M. N. Hughes, 43,
Chapter 3 Electron-transport Proteins By P. M. Handford and W. K. Lee, 78,
Chapter 4 Oxidases and Reductases By A. E. G. Cass and P. F. Knowles, 151,
Chapter 5 Zinc Metalloenzymes By A. Galdes, 216,
Chapter 6 Manganese Metalloproteins and Manganese-activated Enzymes By A. R. McEuen, 249,
Chapter 7 Trace Elements in Animal Nutrition By J. R. Arthur, I. Bremner, and J. K. Chesters, 283,
Chapter 8 Inorganic Elements in Biology and Medicine By N. J. Birch and P. J. Sadler, 315,

CHAPTER 1

Inorganic Analogues of Biological Molecules

C. A. McAULIFFE

1 Complexes of Amino-acids and Peptides

As in Volume 1, this section is divided into three parts, namely metal complexes of (i) simple amino-acids and peptides; (ii) amino-acids containing sulphur donors; and (iii) amino-acids containing heterocyclic nitrogen donors. In searching the literature it is evident that, in only one year, there has been a significant growth in the number of studies of interactions of metal ions with peptides.

Simple Amino-acids and Peptides. — In commenting on the origin of the stereo-selectivity in the condensation of acetaldehyde with glycine co-ordinated to cobalt(III), Phipps suggests that an intermediate exists which has an oxazolidine-type structure similar to the cyclic amino-acid proline. Phipps has also studied the rate constants for the 1H–2H exchange in cobalt(III)-amino-acid complexes as a function of charge and ligand structure. The H–D exchange of α-hydrogens also depends on pH of the solution, temperature, distortion of the valence angle, and the stability of the carbanion intermediate. The crystal structure of L-asparaginato-D-aspartatocobalt(III) monohydrate shows that the amide group of the L-asparaginate ion is co-ordinated through the nitrogen atom and an enolic system of Co<-NH=C(OH) — CH2 — is formed. From X-ray data of (+)546 –cis(O)-triammine (sarcosinate-N-propionato) cobalt(III) (+)546 -(ethylene-diaminetetra-acetato)cobalt(III) monohydrate it is seen that the co-ordinated asymmetric nitrogen atom of sarcosinate-N-propionate takes an (R) configuration. Magnetic circular dichroism (m.c.d.) spectra of [Co(NH3)5- (OCOCHRNH3)]3+, [Co(NH2CHRCO2)(NH3)4]2+, and [Co(NH2CHRCO2)-(en)2]2+ types show that complexes belonging to a given type show nearly identical m.c.d. curves, irrespective of variation in their natural c.d. patterns; the complexes of D-, L-, and DL-alanine show identical m.c.d. spectra.

The ultrasonic absorption of aqueous solutions of nickel(II) complexes of glycine, β-alanine, 4-aminobutyric acid, and 6-aminohexanoic acid has been measured, but the relaxation absorption could not be ascribed to one of the steps of the ordinary step-by-step mechanism of complex formation; however, it may be attributed to the formation-breaking equilibrium of an intramolecular hydrogen bond due to the carboxylato-group of an amino-acid that is coordinated to the nickel(II) ion.

Armeria maritima plants collected from a bog near Dolgellau, and which are highly copper-tolerant, may well contain a copper–proline complex in the roots. Solution equilibria of ternary α-amino-acid–copper(II) complexes which contain electrostatic ligand–ligand interactions show that the protonated ternary species [Cu(L-A)(L-B)(H)] and [Cu(D-A)(D-B)(H)] have essentially the same stability constants (A is aspartic or glutamic acid; B is arginine, lysine, or ornithine). The stability constants of several 1:1 metal complexes of N-phosphonomethyl) glycine(glycophosphate)(the metal is bivalent Cu, Zn, Mn, Ca, or Mg) have been determined. Bis(glycinamide)copper(II), Cu(H-1Ga)2, undergoes direct nucleophilic attack by triethylenetetramine (trien) with a rate constant of 1.4 × 104 mol-1 s-1 at 25 °C; the reactivity of trien with mono(triglycinato)cuprate(II)[Cu(H-2G3)]-, is three orders of magnitude greater. An equilibrium study of mixed-ligand complexes of copper(II) with amino-acids and of 2,2′-bipyridyl with thiophendicarboxylic and pyridinedicarboxylic acids has been reported. Aqueous solutions containing copper(II) ions, pyruvate, and L-(+)-alanine in the molar ratio 1:2:4 give rapid racemization of alanine; the reaction is first-order in the concentration of base; kobs = (5.43 × 10-2) [OH- ]s-1 at 60 °C. In copper(II)-poly(L-ornithine) complexes, in aqueous solution, two complexes exist; complex I contains two amine and two amide nitrogens and complex II contains two amine nitrogens and two water molecules as donors. It is clear that metal–phenolate co-ordination exists in the copper(II)–poly(L-lysine, L-tyrosine) complex, as evidenced by a band at 1320 cm-1 in the resonance Raman spectra. Hamalainen and co-workers have prepared and obtained single-crystal X-ray information on two Schiff-base-amino-acidcontaining complexes: catena-µ-(N-salicylidene-L-tyrosinato-O’,O’-copper(II) is square-pyramidal; the basal plane consists of the terdentate ligand and an oxygen atom of the adjacent carboxylate group, and the other oxygen of the carboxylate group occupies the axial position (Cu — Ob = 198.6 pm, Cu — Oa = 249.1 pm); a similar structure is obtained for the N-salicylidene-L-phenylalaninatoaquocopper(II) dimer, i.e. a terdentate ligand and a water molecule in the basal plane. The crystal structure of the copper(n) complex with the Schiff base derived from (1R)-3-hydroxymethylenecamphor and (S)-phenylalanine shows a quasi-planar O3N co-ordination sphere. The structure of bis-(N-acetylglycinato)diaquocopper(II) dihydrate shows it to be centro-symmetric, the copper atom being surrounded by two oxygen atoms of the water molecules and two oxygen atoms of the carboxylate groups (Cu — O = 194.4 and 195.2 pm, respectively). The magnetic properties of two unusual Schiff-base-copper(II) chelates, i.e. (N-salicylideneglycinato)aquocopper(II) hemihydrate and (N-salicylidene-α-aminoisobutyrato)aquocopper(II), have been measured as a function of temperature (1.6 — 160 K) and applied field strengths (10 — 50 kG), these data revealing that the exchange interaction in [Cu(N-sal=gly)H2O]·½H2O is not between an infinite linear array of copper atoms but is predominantly between pairs of coppers in different structural chains. The interaction of O-phospho-DL-serine, O-phospho-DL-methylserine, O-phospho-DL-threonine, and O-phosphoethanolamine with bivalent copper, nickel, zinc, cobalt, manganese, magnesium, and calcium has been studied by potentiometry and 31P n.m.r. spectroscopy. Equilibrium data indicate that, for the normal 1:1 complexes, the phosphate moiety binds the transition-metal ion, forming a seven-membered chelate ring. However, the 31P n.m.r. evidence shows that this ring is not formed in the normal 1:2 complexes.

A detailed characterization of a series of N– and C-methyl-substituted glycine complexes of platinum(II) reveals both chelated complexes of general formula [Pt(Gly)Cl2]- and unidentate TV-bound complexes of the type [Pt(Gly)(NH3)3]+. Carbon-13 n.m.r. chemical shifts and 195Pt–13C spin–spin coupling constants are instrumental in defining the conformational behaviour of these complexes. Reilly and co-workers have similarly studied both chelated [Pt(amino-acid)-Cl2]- and N-co-ordinated [Pt(amino-acid)(NH3)3]+ species for the amino-acids proline and pipecolic acid. Mixed complexes, trans-[Pt(proO)A] (pro = L-prolinate, A = anion of sarcosine or of the L-enantiomers of alanine, serine, valine, or proline), contain amino-acidate ligands in mutually trans arrangement via oxygen and nitrogen donors. The complex trans-[Pt(proO) (sarO)] has been separated into its diastereoisomeric forms, i.e. trans-[Pt(S-proO)(S-sarO)] and trans-Pt(S-proO)(R-sarO)], where S and R denote the configurations at the asymmetric nitrogen centres. The rates of inversion and of deuteriation at the asymmetric nitrogen centres of sarcosine are kD [much greater than] kinv. Addition of a large excess of trans-2-butene (tbn) or 2-methyl-2-butene (mbn) to a solution of cis– or trans-(N, ethylene) [PtCl(L-am) (C2H4)] (L-am represents any one of nine amino-carboxylate species) in acetone gave initially an increase and then a gradual decrease in c.d. strength in the region 26 500 cm-1, the kinetic optical yield amounting to 53%. trans-2-Butene gives larger yields than mbn. Kinetic analysis of the growth and decay curve of the c.d. strength indicates that the first fast increase in c.d. reflects the greater rate of substitution of the prochiral olefins for ethylene in the (S) configuration than that in the (R) configuration, and the second step involves the exchange of co-ordinated tbn or mbn, catalysed by ethylene freed in the first step.

Spectrophotometric studies have provided evidence for zinc-mediated ternary complexes between ATP and aromatic amino-acids; the hypochromicity observed in the 260 nm band of ATP increased in the order phenylalanine via an amino-group (Hg — N = 2.17 Å) and mercury has further, weaker intramolecular interactions with the carboxylate group (Hg — O = 2.62 Å) and with the phenyl ring (Hg — C = 3.19, 3.33 Å), whilst in the latter complex a phenyl-ring interaction is absent but the amino-group is again bound (Hg — N = 2.15 Å), and mercury has both intramolecular and intermolecular interactions with carboxylate groups (Hg — O = 2.72, 2.78 Å). The hydrolysis of methylmercury(II), the protonation of formic and acetic acids and of glycine, alanine, and valine, and their complex formation with MeHg+ have been studied by a potentiometric method, at 25 °C.

Some nickel(II) complexes of Schiff bases derived from salicylaldehyde and glycyl-aspartate or -glutamate have been isolated. The relationship between the structure of the chelates and the stability of the fused ring systems has been applied to an interpretation of a selective hydrolysis reaction of dimethyl glycylaspartate and glycylglutamate. Further work on the hydrolysis of amino-acid esters (methyl and ethyl 4-aminobutanoate) in cobalt(III) complexes by bases has been reported. A variety of main-group and transition-metal ions have been studied as moderators of the enzymatic hydrolysis of L-asparagine by L-asparaginase; the greatest deactivations were observed by Hg, Cu, and [PdCl4]2- species. Angelici and co-workers have correlated the rates of hydrolysis of amino-acid esters, catalysed by copper(n) complexes, with the stabilities of those complexes. The second-order rate constants, i.e. rate = kDH[Cu(L)(Me-gly)]x+[OH-], for the hydrolysis of a series of methylglycinate complexes have been reported, as have their activation parameters. Terdentate and quadridentate copper(II) chelates fall on different isokinetic lines, suggesting that there are different mechanisms or rate profiles.

The interactions of angiotensin II and a synthetic analogue [Asn1, Val5]-angiotensin II with Ca2+ and Tb3+ have been monitored, using the intrinsic fluorescence of the tyrosine residue at position 4 in both molecules. These data suggest that angiotensin II binds both metals with a dissociation constant of 1 × 10-4 l mol-1; no binding was observed with the amide analogue. Energy transfer is observed between Tb3+ and the tyrosine residue of angiotensin, which indicates that the hydroxyl or the carbonyl group of the tyrosine is close to the metal-binding site. In order to explore the biological application of macrocyclic tetra-amines, the kinetics of the replacement of triglycine on copper(II) by, e.g., 1,4,7,10-tetra-azacyclododecane have been examined. Interest in the possible role of copper(III) in biochemistry has been heightened by the evidence obtained by Hamilton and co-workers for its involvement in galactose oxidase, and, as well as Hamilton’s experiments, resonance Raman spectra of copper(III)–peptide complexes have recently been reported. A novel avenue for the investigation of mechanisms for the specific co-ordination of a metal to a protein is by determining the volume changes, ΔV, that occur during the interaction between metal cations and proteins, as was done recently for the binding of copper(II) to dipeptides.

First-row transition-metal(n) complexes of N-acetyl-DL-valine of the type [M(Ac-Val)2]·xH2O (M = Co or Ni, x =2; M = Zn, x = 0) and their amine adducts of type [M(Ac-Val)2B2]·xH2O (M = Co, Ni, or Zn; B = pyridine, 3- and 4-methylpyridine, or 1,10-phenanthroline) appear to contain hexaco-ordinated cobalt(II) and nickel(II), with some distortion from Oh symmetry (MO6 and MO4N2 chromophores). In one diastereoisomer of [Co(L-Phe-Gly)2] both of the methylene protons of the C-terminal CH2 group are shifted upfield by the ring current of the aromatic ring, whereas in the other diastereoisomer only one of the protons is shifted upfield; comparison of these results with models enables the absolute configuration of the diastereoisomers to be determined. In the tetragonal bivalent nickel, copper, and palladium complexes of Tyr-Gly-Gly and Gly-Leu-Tyr, an interaction between the aromatic ring and the metal is proposed, being most effective for nickel(II). Dimers form in solutions of the copper(II)-Gly-Leu-Tyr complex at pH 8 — 10, and with all three metals the ligands are quadridentate at pH up to 11 and terdentate at higher pH.

Separation, with the aid of a dialysis membrane, of the measuring electrode from the solution to be studied enabled a zinc amalgam electrode system to be developed which is suitable for determining the activity of zinc ion, even in the presence of macromolecules which poison the electrode. Using this apparatus, the binding of zinc to ACTH1-32, which is a fragment of corticotropin (ACTH) consisting of the first 32 amino-acid residues, in aqueous solution, at pH 5.9 has been studied. Molecular oxygen reacts with nickel(II)-peptide complexes in aqueous solution by a facile autocatalytic process in which nickel(III) intermediates play a major role. With tetraglycine, the formation of [NiIII(H-3Gly4)] -initiates the reaction which results in the formation of carbon dioxide, triglycyl-N– (hydroxymethyl)amide, and glycinamide as the main products. In the mixed-ligand complex (2,9-dimethyl-1,10-phenanthroline)(glycylglycinato)-copper(II) pentahydrate, Gly-Gly serves as a terdentate ligand that co-ordinates with its amino-nitrogen (Cu — N = 2.05 Å), its ionized amide-nitrogen (Cu — N = 1.90 Å), and its carboxylate-oxygen (Cu — O = 2.03 Å). A fourth position, completing a distorted square about the copper, is occupied by one of the two nitrogen atoms of dimethylphenanthroline (Cu — N = 2.0 Å), whilst the other nitrogen occupies a nearly apical position in the square pyramid (Cu — N = 2.06 Å). The magnetic properties of the unique nitrogen-bridged dimer sodium glycylglycinatocopper(II) monohydrate, Na2[Cu(Gly-Gly)H2O]2, have been measured as a function of temperature. In αβ-didehydroglycylglycylhistidinatocopper(II) dihydrate the copper atom is square-planar, co-ordinating to four nitrogen atoms of the ligand, there being no weak interaction (<3.0 Å) with any fifth donor atom. The distances Cu — N(amino), Cu — N1 (peptide), Cu — N2-(peptide),and Cu — N(imidazole) are 2.O28, 1.898, 1.960, and 1.941 Å respectively.A major feature of the structure is that the original ligand has undergone an oxidative decarboxylation. Four sequential bond-dissociation steps occur when excess acid reacts with tripeptide (L-) complexes of palladium(II). The dissociation starts at the carboxylate end with a fast reaction (t½<10-3 s) and proceeds through intermediates, where rapid protonation of the peptide oxygens occurs prior to cleavage of the Pd — N (peptide) bond.

(Continues…)Excerpted from Inorganic Biochemistry Volume 2 by H. A. O. Hill. Copyright © 1981 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.