High-performance liquid chromatography and photodiode-array detection of the human protein HC (human complex-forming glycoprotein heterogeneous in charge), a chromophore-associated protein

Identification and quantitation of iodotyrosines and iodothyronines in proteins using high-performance liquid chromatography by photodiode-array ultraviolet-visible detection

We describe a new method for the separation, identification and quantitation of iodotyrosines and iodothyronines [3-monoiodo-L-tyrosine (MIT), 3,5-diiodo-L-tyrosine (DIT), L-thyronine (T0), 3,5-diiodo-L-thyronine (T2), 3,5,3'-triiodo-L-thyronine (T3), reverse 3,3',5'-triiodo-L-thyronine (rT3) and 3,3',5,5'-tetraiodo-L-thyronine (T4)]. Reversed-phase high-performance liquid chromatography (RP-HPLC) was performed on a Nucleosil C8 column with photodiode-array UV-Vis detection. A clearly defined elution profile was obtained of each iodoamino acid (iodotyrosines and iodothyronines) using a linear gradient from 20 to 80% phase B (90% acetonitrile, 10% water, 0.1% TFA), phase A (water, 0.1% TFA, pH 2.0) eluted over 40 min. Iodoamino acid composition was determined, taking into account retention times and spectral characteristics. Thyroid protein samples were digested enzymatically and the complex mixture of IAA was then injected onto the RP-HPLC system. A photodiode-array detector with a dynamic range in the UV-Vis region was used in the HPLC system to monitor the absorbance at different wavelengths continuously, collecting data which were compared with standard samples. Each IAA was quantitated using linear calibration curves obtained at 280 nm. This method allowed identification and quantitation of iodoamino acids from diverse sources in the range 2-500 ng, avoiding the need to radiolabel samples. The technique was tested with in vitro iodinated and non-iodinated human thyroglobulin and the recoveries ranged from 84 to 91%.

Spectroscopic characterization by photodiode array detection of human urinary and amniotic protein HC subpopulations fractionated by anion-exchange and size-exclusion high-performance liquid chromatography

A procedure for spectroscopic characterization and partial fractionation of human protein HC populations by high-performance liquid chromatography-photodiode array ultraviolet-visible detection is reported. Human protein HC from urine or amniotic fluid fractionated by anion-exchange HPLC in a protein Pak DEAE 5PW appeared to be heterogeneous as judged by the asymmetric elution pattern, consisting of a continuous irregular broad peak with several shoulders distributed along the whole chromatogram. Selected fractions containing shoulders were rechromatographed and finally six symmetrical homogeneous peaks with different retention times were obtained from each protein HC preparation. The direct automatic absorption spectra analyses at each peak maximum, indicated that all of the homogeneous peaks seemed to be protein HC, all of them associated to the same chromophore although with different stoichiometry ratios. Isoelectric focusing showed that each peak was composed of a limited number of subpopulations of protein HC with different isoelectric points. Size microheterogeneity has been also demonstrated in both urinary and amniotic protein HC preparations by a combination of size-exclusion HPLC on a TSK 3000 SW6 column and photodiode array detection. Partial fractionation of human albumin on an analytical anion-exchange Mono-Q PC 1.6/5 column, has allowed the identification of heterogeneous chromophore-containing populations displaying significant absorption in the visible region in resemblance to that of protein HC.

Location and characterization of the three carbohydrate prosthetic groups of human protein HC

Three different carbohydrate prosthetic groups associated to three chymotryptic peptides, Q1, Q2 and Q3, were isolated from the reduced and carboxymethylated human protein HC. The first oligosaccharide forms an O-glycosidic linkage with a threonine residue at position 5 in the polypeptide chain of protein HC. The second and third carbohydrate prosthetic groups form N-linkages with asparagine residues at positions 17 and 96. Oligosaccharides present in Q1 contain 1 residue of NANA, 2 of GalNAc and 1 of Gal corresponding to the following structure: -O-GalNAc-GalNAc-Gal-NANA. Q2 contains 3 NANA, 9 GlcNAc, 2 Gal and 3 Man, and Q3 contains 2 NANA, 5 GlcNAc, 1 Gal and 2 Man. The sugar compositions of Q2 and Q3 oligosaccharides are compatible with that of the complex kind. The amount of oligosaccharides present in Q1, Q2 and Q3 corresponded respectively to 3.0%, 12.2% and 7.3% of the weight of protein HC. No difference was found between the carbohydrate composition of urinary and plasma protein HC.

Measurement of protein HC (alpha 1 microglobulin) and protein HC-IgA complex in different body fluids

Protein HC and protein HC-IgA complex were measured in 18 different types of fluid sample from healthy subjects and patients with different illnesses to determine if the concentrations of protein HC and protein HC-IgA complexes could be used to monitor certain diseases, when measured separately. The normal values for HC ranged from between 0.30 mg/l in saliva and 11.7 mg/l in blood plasma. HC-IgA complex has a greater range, from undetectable concentrations (urine, colostrum, and cervical mucus) up to 59.2 mg/l in blood plasma. Undetectable concentrations of HC-IgA complex were also shown in serum from patients with IgA immune deficiency and in cerebrospinal fluid from patients with multiple sclerosis. Increased concentrations of HC were noted in bronchoalveolar fluid from a patient with pulmonary alveolar proteinosis, serum from patients with Behcet's syndrome, and in synovial fluid from patients with gout, chondrocalcinosis, and rheumatoid arthritis. On the other hand, the concentrations of HC-IgA complex were raised only in those patients with pulmonary alveolar proteinosis or rheumatoid arthritis.