The use of HPLC in biotechnology

Analysis of proinsulin and its conversion products by reversed-phase high-performance liquid chromatography

Proinsulin is synthesized in the beta-cells of the endocrine pancreas, one of the four cell types found in the islets of Langerhans. Specific enzymatic cleavage of proinsulin results in the formation of equimolar amounts of insulin and C-peptide, via several intermediate split-proinsulin forms. Most mammals produce a single insulin, but in rodents two non-allelic insulin genes are expressed. There is an inverse ratio between the two insulins in rats and mice, the reason for this being unknown. It has been suggested that differences in transcription, translation (biosynthesis) and/or posttranslational processes (enzymatic conversion, intracellular degradation) could be possible explanations. Elevated amounts of proinsulin-immunoreactive material (PIM) have been described to occur in various conditions/diseases, suggesting alterations in beta-cell function, but the composition of the secreted PIM (intact proinsulin or its intermediates) has been incompletely determined. Studies of the biosynthesis of proinsulins and their conversion with the purpose of revealing some of these points depend on accessible reversed-phase high-performance liquid chromatographic (RP-HPLC) analyses capable of separating all the relevant, closely related polypeptides involved. This review will deal with the optimization of the RP-HPLC separations as well as sample preparation and recovery. Applications of the selected methods in the study of proinsulin biosynthesis and its conversion will also be presented.

Non-ideal behaviour of silica-based stationary phases in trifluoroacetic acid-acetonitrile-based reversed-phase high-performance liquid chromatographic separations of insulins and proinsulins

Several C18 stationary phases were found to behave non-ideally when insulins and proinsulins were eluted with shallow acetonitrile gradients in 0.1% trifluoroacetic acid, resulting in poor peak shapes or no elution at all. With triethylammonium phosphate or ammonium sulphate as buffer components, the insulins and proinsulins were eluted with excellent peak shapes, presumably owing to better masking of residual silanol groups on the stationary phases. Similar use of trifluoroacetic acid-acetonitrile gradients on the less hydrophobic C4 or C3 stationary phases resulted in excellent peak shapes. The difficult separation of rat proinsulin I and II, which are important for the study of rat insulin biosynthesis, was only achieved with two different stationary-mobile phase combinations.

"Glutaraldehyde-P", a stable, reactive aldehyde matrix for affinity chromatography

A high-performance affinity chromatography support based on silica has been developed for the immobilization of proteins containing primary amino groups. A hydrophilic polymer covalently bound to the silica surface minimizes nonspecific protein binding to the support while preserving high binding capacity. The Schiff base reaction involved in the coupling of a ligand to the affinity medium is rapid, allows the use of mild conditions during the coupling process, and results in a very stable linkage. Reaction parameters were studied for protein coupling to the affinity support to determine optimum binding conditions and dynamic capacity as a function of protein size. The stability of the ligand-matrix bond was determined. The performance and reproducibility of the affinity support are demonstrated by its use in the analysis of nitrophenyl sugar derivatives, purification of glycoproteins, and isolation of anti-bovine immunoglobulin G developed in rabbit.