Oxidation of methionine residues in coagulation factor VIIa

The oxidation of the activated form of recombinant coagulation factor VII (FVIIa) by hydrogen peroxide has been studied. The three predominant oxidation products observed at pH 7.5 have been characterized as methionine sulfoxide derivatives of the parent protein involving two of the four methionine residues of the protein, Met298 and Met306. We conclude that oxidation of FVIIa with hydrogen peroxide only affects methionine residues and selectively oxidizes those which are readily accessible to the solvent. The oxidation process has been studied in the pH range 3.5-9.5. The total rate of oxidation of FVIIa as well as the formation of the three oxidation products is consistent over the pH interval 7.5-9.5. However, under acidic conditions, significant variations have been observed indicating a conformational change of FVIIa. Oxidized FVIIa had the same amidolytic activity as the native protein. The binding to soluble tissue factor (TF) was weaker after oxidation as manifested by a threefold increase in dissociation constant and the amidolytic activity in complex with soluble TF was 80% compared to that of native FVIIa. In complex with lipid surface TF, the rate of factor X activation catalyzed by oxidized FVIIa was also reduced by approximately 20% compared to that of native FVIIa. However, native and oxidized FVIIa appeared to bind lipidated TF with indistinguishable affinities.

Improved peptide mapping using phytic acid as ion-pairing buffer additive in capillary electrophoresis

By digestion of the highly basic polypeptide aprotinin or bovine pancreatic trypsin inhibitor (BPTI) with endoproteinase Lys-C after unfolding, reduction and pyridylethylation, five fragments are obtained. These fragments are separated by free solution capillary electrophoresis using a phosphate buffer at neutral pH. The effect of the ion-pairing buffer additive phytic acid on the separation was investigated. It is shown that phytic acid through ion-pair formation influences the mobility of only those peptide fragments having a net positive charge at the pH of the separation buffer. The affinity of phytic acid to the peptides correlates with their isoelectric point and the charge to mass ratios. Hence, by changing the concentration of phytic acid, it is possible to manipulate the migration order and the separation of the peptides.

Analysis of the glycoforms of human recombinant factor VIIa by capillary electrophoresis and high-performance liquid chromatography

The carbohydrate-dependent microheterogeneity of recombinant coagulation factor VIIa (rFVIIa) has been characterized by capillary electrophoresis (CE) of the native protein and by high-performance liquid chromatography (HPLC) of tryptic peptides and of oligosaccharides released by hydrazinolysis. The development of the CE analysis is reported here. We have found that application of 1,4-diaminobutane (putrescine) as additive to the CE separation buffer is essential for the separation of the various glycoforms. Under optimum conditions rFVIIa migrates as a cluster of six peaks or more. By CE of neuraminidase-treated rFVIIa a faster-moving double peak is observed. This indicates that the separation obtained is primarily based upon the different content of N-acetyl-neuraminic acid of the oligosaccharide structures in rFVIIa. By reversed-phase HPLC of tryptic digested neuraminidase treated rFVIIa the glycopeptides containing the heavy chain N-glycosylated site elute as two peaks compared to the four peaks corresponding to glycopeptides with 0 to 3 N-acetyl-neuraminic acids seen for untreated rFVIIa. In high-pH anion-exchange HPLC of the oligosaccharides released from native rFVIIa by hydrazinolysis the major peaks elute as oligosaccharides with 1 or 2 N-acetyl-neuraminic acids. Oligosaccharides released from neuraminidase treated rFVIIa elute earlier compared to oligosaccharides from native rFVIIa, but separated into several peaks, indicating heterogeneity for the oligosaccharide structures without N-acetyl-neuraminic acid.

Effective ion-pairing for the separation of basic proteins in capillary electrophoresis

The addition of the sodium salt of phytic acid to the separation buffer (pH's 6.0-9.5) has allowed the analysis of a number of basic proteins (pI's > 9) by capillary electrophoresis. The method of analysis is simple and leads to considerable improvement in peak shape. Some very basic proteins, totally adsorbed onto the capillary fused silica surfaces in the presence of buffer only, can be analysed as sharp signals when this polyanionic species is included in the running electrolyte. These improvements in analysis are thought to arise as a result of the suppression of coulombic interactions between these positively charged proteins (ion-paired to phytic acid) and the negatively charged silanol groups on the inner wall of the capillary.

Characterization of glycopeptides from recombinant coagulation factor VIIa by high-performance liquid chromatography and capillary zone electrophoresis using ultraviolet and pulsed electrochemical detection

Four glycopeptide (GP) fractions containing glycosylated Asn 322 were isolated from a tryptic digest of recombinant coagulation factor VII by reversed-phase-HPLC (RP-HPLC). Characterization of the GPs by enzymatic desialylation and RP-HPLC as well as by enzymatic deglycosylation, RP-HPLC, and high-pH anion-exchange chromatography indicated that the four GPs consisted of the same decapeptide but with 0, 1, 2, or 4 residues of sialic acid. In comparison to HPLC, capillary zone electrophoresis (CZE) using uv and pulsed electrochemical detection (PED) afforded improved separation of GPs from each other and from contaminants. CZE-uv and CZE-PED of the desialylated GPs and deglycosylated GPs corroborated the results obtained with the chromatographic methods.