James O. Alben

Pi-interactions in metalloporphyrins and hemeproteins.

Pi-interactions have played an important role in the development of ideas about porphyrin, metalloporphyrin, and hemeprotein systems. In early studies of the isolation, structure and synthesis of porphyrins, “molecular complexes” such as picrates and flavianates were widely used.”* The tendency for hemins to associate in solution was also studied in some detail, although it is still not well under~ t o o d ; ~ ’ ~ and pi-bonding between iron and axial ligands was introduced to describe bonding of several ligands to iron porphyrins and he me protein^.^ Recent experiments have provided evidence for pi-interaction between the central metal ion and axial ligands, between the metal ion and the porphyrin, and between the porphyrin pi-electron system and the solvent and/or protein environment.

Recent studies of the cytochrome o terminal oxidase complex of Escherichia coli

The cytochrome o complex is the predominant terminal oxidase in the aerobic respiratory chain of Escherichia coli when the bacteria are grown under conditions of high aeration. The oxidase is a ubiquinol oxidase and reduces molecular oxygen to water. Electron transport through the enzyme is coupled to the generation of a protonmotive force. The purified cytochrome o complex contains four or five subunits, two protoheme IX (heme b) prosthetic groups, plus at least one Cu. The subunits are all encoded by the cyo operon. Sequence comparisons show that the cytochrome o complex is closely related to the aa3-type cytochrome c oxidase family. Gene fusions have been used to define the topology of each of the gene products. Subunits I, II, III and IV are proposed to have 15, 2, 5 and 3 transmembrane spans, respectively. The fifth gene product (cyoE) encodes a protein with 7 membrane spanning segments, and this may also be a subunit of this enzyme. Fourier transform infrared spectroscopy has been used to monitor CO bound in the active site where oxygen is reduced. These data provide definitive proof that the cytochrome o complex has a heme-copper binuclear center, similar to that present in the aa3-type cytochrome c oxidases. Site-directed mutagenesis is being utilized to define which amino acids are ligands to the heme iron and copper prosthetic groups.

Photoperturbation of the heme a3-CuB binuclear center of cytochrome c oxidase CO complex observed by Fourier transform infrared spectroscopy

Purified cytochrome c oxidase CO complex from beef heart has been studied by Fourier transform infrared absorbance difference spectroscopy. Photolysis at 10-20 Kelvin results in dissociation of a3FeCO, formation of CuBCO, and perturbation of the a3-heme and CuB complex. The vibrational perturbation spectrum between 900 and 1700 cm-1 contains a wealth of information about the binuclear center. Appearance in infrared photoperturbation difference spectra of virtually all bands previously reported from resonance Raman spectra indicate the importance of polarization along the 4-vinyl:8-formyl axis, which results in the reduction of heme symmetry to C2v. Frequency-shifted bands due to the 8-formyl and 4-vinyl groups of the a3-heme have been identified and quantitated. The frequency shifts have been interpreted as being due to a change in porphyrin polarization with change in spin state of the iron by photodissociation of CO or perturbation of the CuB coordination complex.

Fitting kinetic data for two independent saturable terms by multifit ii, a general purpose curve fitting program in fortran iv☆

Abstract The present report describes multifit ii , a fortran program for fitting data to non-linear equations and its application to biphasic kinetic data. Biphasic plots are encountered, e.g. in cases of enzymatic reactions and in the area of amino acid transport across biological membranes. This program gives a least squares fit of an equation to data, and obviates the need for non-statistical approximations, with their inherent bias. Equations to be fit are written in the form (numerator)/(denominator), where each may contain up to four terms, and each term may be a maximum of fourth order, including up to four independent variables. Data may be fit by the present program in either direct or reciprocal form. The approach taken is an iterative procedure (Newtons method). Scaling and weighting of data are incorporated. Parameters used to generate ideal test data in biphasic kinetic plots were recovered to four significant figures. The utility of the program in fitting real biphasic data obtained from amino acid transport experiments is demonstrated.

Fourier transform infrared spectroscopic study of molecular interactions in hemoglobin

Infrared absorption spectra of the alpha-104 (G11) cysteine SH group have been observed for aqueous solutions of hemoglobin derivatives from humans, pigs, and horses. The center frequencies ((nu)SH) show ligand sensitive patterns that are similar for the three species, with (nu)SH (HbCO) <(nu)SH (HbO(2) ~ HbCN) < (nu)SH (Hb(+)) <<(nu)SH (deoxyHb) for human and pig hemoglobins. The alpha-104 SH group is most strongly H-bonded (smallest (nu)SH), has the greatest range of (nu)SH (Hb ? HbCO) in human hemoglobin, and is least strongly H-bonded and has the smallest range of (nu)SH (Hb ? HbCO) in horse hemoglobin. The beta-112 cysteine SH in human hemoglobin is more weakly H-bonded than is the alpha-104 SH. These studies illustrate how FTIR can be used to measure differences in protein structure that are related to biological control mechanisms.

Spectrophotometric determination of monophenolase activity of tyrosinase isozymes

Mushroom tyrosinase (EC 1.10.3.1, o-diphenol: oxygen oxidoreductase) was partially purified and the oxidation of p-cresol studied. The conditions were established for a spectrophotometric determination of monophenolase (cresolase) activity, based on measurements of initial velocity. Tyrosinase isozymes were separated by high-resolution column chromatography on Sephadex A-50 (DEAE), and distinguished by substrate specificities. The ratio of classical manometric cresolase units (13) to spectrophotometric units was 3.85 for all isozymes.

FOURIER TRANSFORM INFRARED SPECTROSCOPY OF HEMOGLOBIN1

Fourier transform infrared spectroscopy has become a powerful probe of local molecular structure in biological macromolecules. Vibrational absorption bands from each of the cysteine SH groups in hemoglobin have been identified and studied by use of aqueous solutions of human, pig, horse, and cow hemoglobin, and isolated α-chains. The vibrational absorption band frequency of α-104 cysteine SH is highly sensitive to change in α-chain tertiary structure and quaternary structure of the tetramer, and is modulated by the heme-ligand complex in the sequence, HbCO 2 ˜ HbCN) + −1 and 1107 cm −1 by Fermi resonance with the iron-oxygen vibrational overtone. This strong vibrational coupling is associated with a polarized covalent iron-oxygen bond.

The highly conserved methionine of subunit I of the heme-copper oxidases is not at the heme-copper dinuclear center: Mutagenesis of M110 in subunit I of cytochrome bo3-type ubiquinol oxidase from Escherichia coli

A common feature within the heme‐copper oxidase superfamily is the dinuclear heme‐copper center. Analysis via extended X‐ray absorption fine structure (EXAFS) has led to the proposal that sulfur may be bound to CUB, a component of the dinuclear center, and a highly conserved methionine (M110 in the E. coli oxidase) in subunit I has been proposed as the ligand. Recent models of subunit I, however, suggest that this residue is unlikely to be near CUB, but is predicted to be near the low spin heme component of the heme‐copper oxidases. In this paper, the role of M110 is examined by spectroscopic analyses of site‐directed mutants of the bo 3‐type oxidase from Escherichia coli. The results show that M110 is a non‐essential residue and suggest that it is probably not near the heme‐copper dinuclear center.

Photochemical dissociation in optically dense solutions: applications to photolyzed carboxymyoglobin (Mb*CO)

Photodissociation of ligands has made important contributions to the understanding of function and structure of heme proteins. Here we present a theory for photochemical dissociation that is not limited by the assumption of previous analyses of optically thin samples, and apply it to interpretation of the photodissociated state of carboxymyoglobin (Mb*CO). Equations are derived and presented in terms of the effects of absorbance, [log10(I0/I) = A, the probability of absorption of light quanta per unit surface area], and the potential for dissociation, D (maximum probability of photodissociation per unit surface area; a linear function in time of photolysis), for both monochromatic and polychromatic light sources. When monochromatic light is used, we show that for large absorbances (A > 2) the fractional photolysis increases as (log D)/A, and may appear to “saturate” even though well below completion. For polychromatic light intensities and absorbances, the theory predicts that the near-infrared tail of the absorbance band of carboxymyoglobin should be sufficiently transparent to allow the radiation to penetrate the sample, yet still have a significant absorptivity such that complete photodissociation is possible. An optically thick myoglobin-CO sample illuminated with a tungsten lamp was observed to behave somewhere between these two theories. These theoretical relations may be useful in the analysis of photolysis data from optically dense solutions and as a guide for future experimental design.

FT-IR analysis of membranes of Rhodobacter sphaeroides 2.4.3 grown under microaerobic and denitrifying conditions

Fourier transform infrared spectroscopic analysis of CO binding proteins in Rhodobacter sphaeroides reveals the presence of a membrane-bound nitric oxide reductase (Nor). Nor has been clearly distinguished from the cytochrome oxidases by the temperature-dependence of relaxation following photodissociation of the CO complex at cryogenic temperatures. The center frequency and band shape, 1970 cm-1 and 20-30 cm-1 width at half-peak height, are similar to those reported for resonance Raman spectra of purified Paracoccus denitrificans Nor. Additional evidence is presented to indicate this enzyme is part of dissimilatory nitric oxide metabolism and that one of the genes in the nor operon required for production of an active Nor is not required for protein assembly or heme incorporation.