Recent developments in protein chromatography involving hydrophobic interactions

Hydrophobic interaction chromatography of proteins

In this article, an overview of hydrophobic interaction chromatography (HIC) of proteins is given. After a brief description of protein hydrophobicity and hydrophobic interactions, we present the different proposed theories for the retention mechanism of proteins in HIC. Additionally, the main parameters to consider for the optimization of fractionation processes by HIC and the stationary phases available were described. Selected examples of protein fractionation by HIC are also presented.

Haemocompatibility of invasive sensors

In recent years the importance and utilisation of invasive chemical sensors have increased, especially in respect to their function and behaviour in a biological environment. This review aims to highlight the development of various sensors and reflect on the problems which can occur when the sensors come into contact with blood. Thus their haemocompatibility is a key area of importance. A clear understanding of their interaction with plasma proteins at the point of interface is fundamental as this determines their ultimate capability to function safely and effectively. There is also an overview of various techniques that have been developed, together with a broad summary of inherent problems which may arise when aiming to improve the haemocompatibility of invasive sensors for in vivo applications.

Novel Ca2+-activated neutral protease from an aquatic fungus, Allomyces arbuscula

A Ca2+-activated neutral protease was purified to homogeneity from an aquatic Phycomycete fungus, Allomyces arbuscula. It requires millimolar concentrations of Ca2+ for activation (1.8 to 2 mM for 50% activation). Sr2+ can replace Ca2+ but at higher concentrations (4 mM for 50% activation). The enzyme is a dimer of 40-kilodalton subunits and contains six cysteine residues, three of which are revealed only after the addition of micromolar concentrations of Ca2+; the other three are free. Enzyme activity is strongly inhibited by SH-group inhibitors and some trypsin inhibitors (leupeptin and alpha-N-tosyl-L-lysine chloromethyl ketone). The enzyme lacks general trypsinlike specificity, since substrates containing tryptic cleavage sites are not cleaved nor is enzyme activity inhibited by other trypsin inhibitors. The enzyme has many functional similarities to the extensively characterized mammalian and avian Ca2+-activated neutral proteases but differs in its substrate specificity, inhibition by alpha-N-tosyl-L-phenylalanine chloromethyl ketone, and subunit structure. It is, nevertheless, presumed that this enzyme has a similar high order of specificity and is involved in the regulation of a specific growth function.

The effects of chemical modification of calmodulin on Ca2+-induced exposure of a hydrophobic region. Separation of active and inactive forms of calmodulin

Native calmodulin binds four calcium ions per molecule and exhibits strong Ca2+-dependent binding to phenyl-Sepharose. In contrast, calmodulin inactivated by oxidation of methionine residues or by deamidation binds fewer calcium ions (two per molecule) and shows relatively weak interaction with phenyl-Sepharose. Calmodulin inactivated by modification of lysine residues still is able to bind four calcium ions per molecule and shows strong binding to phenyl-Sepharose similar to native calmodulin. The results suggest that complete exposure of calmodulin's hydrophobic region occurs only after the binding of four ions of calcium to the calmodulin molecule. Thus, phenyl-Sepharose hydrophobic interaction chromatography might be used to separate active calmodulin from inactive forms of calmodulin obtained by oxidation or heat treatment for prolonged periods. As an example, phenyl-Sepharose chromatography can be used to separate free iodide and inactivated species of calmodulin readily from the active, iodinated form of calmodulin following iodination.

Chromatographic depletion of lipoproteins from plasma and recovery of apolipoproteins

Selective adsorption of proteins from a complex mixture onto an affinity support presents a very powerful approach to protein purification. High density lipoprotein (HDL) and low density lipoprotein (LDL) have been removed from plasma by hydrophobic adsorption chromatography using phenyl-Sepharose. Plasma chromatographed on phenyl-Sepharose is depleted of beta-lipoprotein and apolipoproteins A-I, A-II and E. Less than 5% of the initial amounts of cholesterol, triacylglycerol, sphingomyelin, and phosphatidylcholine remain in the plasma. Column elution with propylene glycol permits recovery of apolipoproteins A-I, A-II and E. This procedure should provide a convenient alternative to ultracentrifugal removal of lipoproteins from plasma.

A quantitative study of the biospecific desorption of rat liver (M4) lactate dehydrogenase from 10-carboxydecylamino-Sepharose. Determination of the number of ligand-binding sites blocked on adsorption

1. The theory of Nichol, Ogston, Winzor & Sawyer [(1974) Biochem. J. 143, 435-443] for quantitative affinity chromatography, when adapted for use with a non-specific column from which a multi-site protein can be specifically desorbed by its free ligand, permits determination of the concentration of adsorption sites on the column, their adsorptive affinity (as an association constant) and either the intrinsic (site) constant for ligand-binding to the protein or an 'occlusion coefficient' (defined as the number of ligand-binding sites blocked on adsorption), one of which must be known. 2. The theory has been applied to the NADH-specific desorption of rat liver M4 lactate dehydrogenase from 10-carboxydecylamino-Sepharose. It suggests that most of the enzyme molecules are adsorbed with at least two NADH-binding sites blocked, indicating an extensive adsorption interface in relation to the protein surface. Other chromatographic parameters were also determined for the system. 3. Among topics discussed are (a) factors affecting the experimentally determined value for the number of blocked sites, (b) the nature of the adsorption sites on the column and (c) the similarity of the analysis to that for determining Hill coefficients, and other possible applications.

Alkyl and omega-amino alkyl agaroses as probes of light-induced changes in phytochrome from pea seedlings (Pisum sativum cv. Alaska)

Partially purified phytochrome from peas (Pisum sativum cv. Alaska) was absorbed to alkyl and omega-amino alkyl agaroses varying in the number of carbons in their alkyl chains from 2 to 10. The absorption and the elution of the absorbed phytochrome from them with KCl, KI, ethylene glycol and surfactants were investigated either in the dark or under red light in order to detect any chemical differences between the red-light-absorbing form of phytochrome (Pr) and the far-red-light-absorbing form of phytochrome (Pfr). With increasing alkyl chain length, more phytochrome was absorbed to the substituted agaroses. Phytochrome was absorbed to a greater extent by alkyl agaroses than by the less hydrophobic omega-amino alkyl agaroses. Absorbed Pfr was eluted by all the eluants tested to a lesser extent than the absorbed Pr. In those cases in which phytochrome could be eluted by KCl, a higher concentration was required to elute Pfr than Pr. As the chain length of the alkyl groups was increased, the difference in elution of Pr and Pfr by KCl increased. Phytochrome was salted out at a lesser concentration of ammonium sulfate after brief red-light irradiation than in the dark. Absorption of phytochrome to DEAE-agarose was also investigated as an example of ionic phytochrome-ligand interactions. The difference between the affinity of Pr and Pfr for DEAE-agarose was less than it was for omega-amino alkyl or alkyl agarose. It is concluded that Pfr is more hydrophobic than Pr.

Hydrophobic interactions of cytochrome c oxidase. Application to the purification of the enzyme from rat liver mitochondria

The binding of rat liver cytochrome c oxidase to phenyl-Sepharose and various alkyl and omega-aminoalkyl agarose gels has been studied. Deoxycholate-solubilized cytochrome c oxidase was tightly bound to hexyl, octyl, omega-aminohexyl, omega-aminooctyl agarose as well as to phenyl-Sepharose. This hydrophobic interaction was used for the purification of cytochrome c oxidase. The enzyme which was eluted from phenyl-Sepharose was devoid of NADH (NADPH)-acceptor reductase activities. The heme a content was 15.4 nmol per mg of protein. The purified enzyme was resolved into seven polypeptides upon polyacrylamide gel electrophoresis in sodium dodecylsulfate with molecular weights of 40,000, 23,200, 21,500, 14,500, 12,600, 8900, and 4900. Antibodies raised in rabbits against the pure enzyme did not cross-react with cytochrome c oxidases from either beef heart or yeast mitochondria. Cytochrome c oxidase bound to octyl-Sepharose or phenyl-Sepharose exhibited a very low catalytic activity. The possible modes of interaction of cytochrome c oxidase with the hydrophobic ligands are discussed.