The analysis of nanogram levels of free amino acids by reverse-phase high-pressure liquid chromatography

Study of the primary structure of recombinant tissue plasminogen activator by reversed-phase high-performance liquid chromatographic tryptic mapping

Two high-resolution tryptic maps have been developed for recombinant tissue plasminogen activator (rt-PA) that separate the expected 51 tryptic peptides. The trypsin digestion was performed after reduction and S-carboxymethylation of the protein. The high-performance liquid chromatographic separation of the tryptic peptides used a Nova-Pak C18 (5 microns) column with a mobile phase that contained 0.1% aqueous trifluoroacetic acid (TFA) or 50 mM sodium phosphate (pH 2.85) and a linear gradient of acetonitrile. A TFA solvent system was also used for re-purification and for characterization of the peptides isolated from the phosphate-based separation. All of the isolated peptides had compositions consistent with the sequence proposed for rt-PA. The identities of the glycopeptides were confirmed by lectin chromatography on concanavalin A-Sepharose. The mixture of tryptic peptides was also treated with endo-beta-N-acetylglucosaminidase H and peptide:N-glycosidase F to locate the position of either high mannose or complex oligosaccharides. These studies demonstrated that a high mannose oligosaccharide is attached to Asn-117 while complex carbohydrate side-chains are attached to Asn-184 and Asn-448. The residue Asn-184 is the site of optional glycosylation that results in the formation of two rt-PA variants that contain either two or three oligosaccharides.

High-performance liquid chromatographic quantitation of collagen biosynthesis in explant cultures

The capacity of lung explant cultures to synthesize collagen can be estimated by determining the content of [3H]hydroxyproline in protein following incubation with [3H]proline. The technique requires acid hydrolysis followed by quantitative separation of hydroxyproline from proline for scintillation counting and is often restricted to methods that can accommodate large samples because of relatively low specific radioactivity. A method which is useful for such samples, providing rapid separation of nonderivatized amino acids by ion-exchange HPLC, is described here. The HPLC system employs an HPX-87C cation-exchange column in 10 mM calcium acetate, pH 5.5, at 85 degrees C. Under isocratic conditions hydroxyproline is completely resolved from proline with quantitative recovery of the 3H cpm applied to the column. Large amounts of material, equivalent to at least 150 mg wet wt of lung, can be applied without affecting resolution or recovery, and samples can be injected at intervals as short as 40 min. This method was used to study collagen biosynthesis in a model of pulmonary fibrosis induced in rabbits by the tumor-promoting agent, phorbol myristate acetate (PMA), and provides information concerning total protein synthesis as well as production of collagen. The data show a doubling in the rate of collagen production in lung explants prepared from animals treated with PMA compared with explants from control animals.

Direct determination of phenylalanine in serum extracts of phenylketonuria patients by reversed-phase high-performance liquid chromatography

A method for direct determination of phenylalanine (Phe) in serum extract by reversed-phase high-performance liquid chromatography with an octadecylsilane column has been devised. Phe is monitored at 220 nm with a UV detector. The mobile phase is a mixture of methanol and water (10:90) with added phosphoric acid and potassium dihydrogen phosphate and has a pH value of 4.3. The minimum detectable amount is 6 ng. The average contents of Phe found for healthy adults and children are 12 and 15 micrograms/ml respectively. Phe contents of sera of three phenylketonuria children are about 10 to 15 times higher than these values.

Amperometric detection of amino acids in high-performance liquid chromatography with a copper electrode

A copper electrode has been used as an amperometric detector for amino acids in high-performance liquid chromatography. The amino acids are separated in a reversed-phase system, using silica-based and polymer-type column materials. Neutral or alkaline buffer solutions of phosphate and carbonate can be used as mobile phases. Borate buffers are less suitable. The detection method is characterized by a high linear dynamic range, good reproducibility, the absence of electrode poisoning and a sensitivity comparable to that of UV absorption methods after derivatization of the amino acids. Detection limits with conventional-scale columns are in the range 10-100 pmoles. A reduction in the flow-rate in the flow-through cell improves the sensitivity for amino acids that give relatively low signals, such as proline. Therefore, the use of microbore columns is especially advantageous for these compounds. The absolute detection limits decrease by about one order of magnitude on changing to a miniaturized system.