Use of immobilized light-harvesting chlorophyll a/b protein to study the stoichiometry of its self-association

Procedure for rapid isolation of photosynthetic reaction centers using cytochrome c affinity chromatography

Horse heart cytochrome c linked to Sepharose 4B is used to purify reaction centers from Rhodopseudomonas sphaeroides R-26. This procedure allows for an initial recovery of 80-90% of the bacterial reaction centers present in chromatophore membranes. High purity reaction centers (A(280)/A(802) < 1.30) can be obtained with a 30% recovery. Reaction centers from wild-type Rps. sphaeroides and Rps. capsulata also bind to a cytochrome c column. Cytochrome c affinity chromatography can also be used to isolate photosystem I complexes from spinach chloroplasts.

Quantitative reappraisal of general expressions for multivalent protein binding in subunit-exchange chromatography

Quantitative expressions have been derived for bivalent equilibria with immobilized ligand systems and for the equilibria for an immobilized protein whose self-association is modified by binding with a soluble ligand, as analyzed by affinity chromatography. These general expressions have been applied in a reexamination of multivalency in the affinity chromatography of antibodies, as reported by Eilat and Chaiken (Biochemistry 18 (1979) 790) and also to studies of neurophysin-peptide hormone interactions using glass matrices reported by Swaisgood and Chaiken (Biochemistry 25 (1986) 4148).

Interaction between immobilized and soluble protein subunits. Analysis and applications

A distinctive property of oligomeric and self-associating proteins is the high specificity of the subunit recognition process. Protein subunits immobilized covalently on a solid matrix maintain this characteristic and are able to bind soluble subunits of the same or a closely related protein under conditions that allow the establishment of a finite association/dissociation equilibrium. The basic theory for studying the immobilized-soluble subunit interaction is presented together with the methodology for a proper protein immobilization. Specific examples are discussed to illustrate on the one hand benefits and caveats of using immobilized protein subunits to measure interaction constants, and on the other preparative applications of subunit affinity columns.

Biospecific interactions: their quantitative characterization and use for solute purification

Biospecificity is due largely to the formation and dissociation of non-covalent complexes between small molecules and macromolecules, or between two macromolecules. The first part of this review is concerned with the use of such biospecificity in the fractionation and identification of solutes. Major emphasis is given to affinity chromatography, especially in regard to the practical considerations inherent in an experimental situation and to the wide range of specific interactions that can be utilized. The second part of the review considers the quantitative characterization of biospecific complex formation. The merits of frontal gel chromatography, electrophoretic methods and affinity chromatography are discussed, and special consideration is given to the effects of ligand and/or acceptor multivalency because of its relevance to many biospecific interactions. Finally attention is drawn to the feasibility of employing quantitative affinity chromatographic theory for the determination of association constants for antigen-antibody systems by radioimmunoassay and enzyme-linked immunosorbent assay techniques.

Preparation and properties of the water-soluble chlorophyll-bovine serum albumin complexes

By mixing chlorophyll (Chl) a or b with a dense bovine serum albumin solution, the water-soluble Chl-bovine serum albumin complexes were prepared. These complexes, eluted near the void volume on a gel filtration, were separated well from unreacted bovine serum albumin, indicating an aggregation of such molecules in the complexes. Preparation of chlorophyllide (Chlide) a- or Chlide b-bovine serum albumin complex was unsuccessful, while the phytol-, and beta-carotene-bovine serum albumin complexes could be obtained. Chls in the Chl-bovine serum albumin complexes had the following characteristics. Main absorption peak of Chl a or b in the red region occurred at 675 nm or 652 nm, respectively. The Chl a-bovine serum albumin complex having absorption peak at 740 nm was also prepared. As compared with the stabilities of Chl a and b in Triton X-100. Both Chls in the bovine serum albumin-complexes were stable against oxidative stresses, such as photobleaching, Fenton reagent, peroxidase-H2O2 system. But they were easily hydrolyzed by chlorophyllase. These properties of Chls in the bovine serum albumin-complexes were similar to those of Chls in the isolated light-harvesting Chl a/b protein complex. A possible localization of Chls within the bovine serum albumin complexes was suggested that the porphyrin moiety of Chl was buried in bovine serum albumin; however, the hydrophilic edge of porphyrin ring, adjacent to the phytol group, occurred in the hydrophilic region of a bovine serum albumin molecule.

Subunit-exchange chromatography of self-associating proteins: a quantitative reappraisal

A quantitative expression describing the behavior of a self-associating protein in subunit-exchange chromatography is derived in a form that is tractable from the viewpoint of characterizing the pertinent interactions. Its use is illustrated by application to published results for alpha-chymotrypsin, oxyhemoglobin, and the light-harvesting chlorophyll a/b protein.

Renaturation studies of free and immobilized D-amino-acid oxidase

The renaturation of free and Sepharose-immobilized D-amino-acid oxidase (D-amino-acid:oxygen oxidoreductase (deaminating), EC 1.4.3.3), after its denaturation with 6 M guanidine hydrochloride, was investigated. No reactivation, or extremely limited reactivation (less than or equal to 4+), was obtained with the free enzyme, is spite of various attempts including the use of dialysis or buffers containing cofactors, different types of anions, surfactants and low concentrations of denaturing agents. The main obstacle to renaturation appeared to be the interaction among denatured or partially renatured monomers giving rise to inactive aggregates. In contrast, using the immobilized enzyme approach, substantial renaturation (up to 50%) of D-amino-acid oxidase was achieved. The denaturation-renaturation process was followed by monitoring the catalytic activity as well as the intrinsic protein fluorescence. An inverse correlation was found to exist between the degree of matrix activation by CNBr and the yield of enzyme reactivation. The anions of the lyotropic series markedly influenced the reactivation, showing an effectiveness opposite to their salting-out potential (thiocyanate congruent to iodide greater than chloride greater than phosphate congruent to sulphate congruent to citrate). Instead, the anions considerably increased the activity and stability of free and immobilized enzyme, according to their salting-out potential. Immobilized monomers of D-amino-acid oxidase, which in solution undergoes self-association, showed poor capacity to interact with the free enzyme: thus they appear unsuitable for analytical and preparative purposes.

The structure of membrane crystals of the light-harvesting chlorophyll a/b protein complex

Membrane crystals of the light-harvesting chlorophyll a/b protein complex from pea chloroplasts were investigated using electron microscopy and image analysis. The membrane crystals formed upon precipitation of the detergent-solubilized complex with mono- and divalent cations in the presence of small amounts of Triton X-100. The crystalline fraction contained two polypeptides of 25,000 and 27,000 mol wt. Freeze-dried and freeze-etched specimens showed a periodic honeycomb structure on the surface of membrane crystals. Double replicas of freeze-fractured sheets showed a hexagonal lattice of particles on both fracture faces. Image analysis of negatively stained membrane crystals suggested that they had threefold rather than sixfold symmetry in projection. A projection map at 20-A resolution revealed two triangular structural units of opposite handedness per crystallographic unit cell. The structural units appeared to be inserted bidirectionally into the membrane, alternating in orientation perpendicular to the membrane plane.

Adhesion between liposomes mediated by the chlorophyll a/b light-harvesting complex isolated from chloroplast membranes

A highly purified chlorophyll a/b light-harvesting complex (chl a/b LHC; chl a/b ratio 1.2) was obtained from Triton-solubilized chloroplast membranes of pea and barley according to the method of Burke et al. (1978, Arch. Biochem. Biophys. 187: 252--263). Gel electrophoresis of the cation-precipitated chl a/b LHC from peas reveals the presence of four polypeptides in the 23- to 28-kdalton size range. Three of these peptides appear to be identical to those derived from re-electrophoresed CPII and CPII* bands. In freeze-fracture replicas, the cation-precipitated chl a/b LHC appears as a semicrystalline aggregate of membranous sheets containing closely spaced granules. Upon removal of the cations by dialysis, the aggregates break up into their constituent membranous sheets without changing their granular substructure. These membranous sheets can be resolubilized in 1.5% Triton X-100, and the chl a/b LHC particles then reconstituted into soybean lecithin liposomes. Freeze-fracture micrographs of the reconstituted chl a/b LHC vesicles suspended in a low salt medium reveal randomly dispersed approximately 80-A particles on both concave and convex fracture faces as well as some crystalline particle arrays, presumably resulting from incompletely solubilized fragments of the membranous sheets. Based on the approximately 80-A diameter of the particles, and on the assumption that one freeze-fracture particle represents the structural unit of one chl a/b LHC aggregate, a theoretical mol wt of approximately 200 kdalton has been calculated for the chl a/b LHC. Deep-etching and negative-staining techniques reveal that the chl a/b LHC particles are also exposed on the surface of the bilayer membranes. Addition of greater than or equal to 2 mM MgCl2 or greater than or equal to 60 mM NaCl to the reconstituted vesicles leads to their aggregation and, with divalent cations, to the formation of extensive membrane stacks. At the same time, the chl a/b LHC particles become clustered into the adhering membrane regions. Under these conditions the particles in adjacent membranes usually become precisely aligned. Evidence is presented to aupport the hypothesis that adhesion between the chl a/b LHC particles is mediated by hydrophobic interactions, and that the cations are needed to neutralize surface charges on the particles.