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A full-length human N-acetylgalactosamine-4-sulphatase (4-sulphatase) cDNA clone was constructed and expressed in CHO-DK1 cells under the transcriptional control of the Rous sarcoma virus long terminal repeat. A clonal cell line expressing high activities of human 4-sulphatase was isolated. The maturation and processing of the human enzyme in this transfected CHO cell line showed it to be identical with that seen in normal human skin fibroblasts. The high-uptake precursor form of the recombinant enzyme was purified from the medium of the transfected cells treated with NH4Cl and was shown to be efficiently endocytosed by control fibroblasts and by fibroblasts from a mucopolysaccharidosis type-VI (MPS VI) patient. Enzyme uptake was inhibitable by mannose 6-phosphate. After uptake, the enzyme was processed normally in both normal and MPS VI fibroblasts and was shown both to correct the enzymic defect and to initiate degradation of [35S]sulphated dermatan sulphate in MPS VI fibroblasts. The stabilities of the recombinant enzyme and enzyme from human fibroblasts appeared to be similar after uptake. However, endocytosed enzyme has a significantly shorter half-life than endogenous human enzyme. The purified precursor 4-sulphatase had a similar pH optimum and catalytic parameters to the mature form of 4-sulphatase isolated from human liver.

Direct comparison of type X collagen synthesized by human, sheep and chick growth-plate cartilage has shown that the human type X collagen is similar to the chick in both its molecular mass, containing component alpha-chains of 59 kDa with helical regions of 45 kDa, and apparent absence of disulphide-stabilized aggregates, whereas the sheep type X collagen has slightly larger alpha-chains (63 kDa) accounted for by a longer helical region (49 kDa) that contains cystine residues essential for the formation of the high-molecular-mass aggregates found with this species. Type X collagen from all three species showed heterogeneity in primary collagen structure as revealed by Staphylococcus aureus V8 proteinase-generated peptide maps. Collagen synthesis by growth-plate cartilage in culture, particularly synthesis of type IX and X collagen, was shown to be very sensitive to prior storage and suggests caution in the interpretation of changes detected when examining collagen synthesis by growth plates in culture.

alpha-L-Iduronidase synthesis and maturation were analysed in fibroblasts from normal controls and from alpha-L-iduronidase-deficient mucopolysaccharidosis-type-I (MPS-I) patients. Fibroblasts were radiolabelled with [3H]leucine and alpha-L-iduronidase was isolated from cell lysates or culture medium by monoclonal-antibody affinity chromatography. Pulse-chase labelling of normal control fibroblasts showed that alpha-L-iduronidase was synthesized as an 81 kDa precursor and processed within 24 h via intermediates of 76 kDa and 70 kDa to a 69 kDa species. The incorporation of radiolabel into alpha-L-iduronidase in fibroblasts from three of four MPS-I patients was at levels that were either very low or undetectable. Fibroblasts from one MPS-I patient, however, exhibited levels of incorporation of radiolabelled amino acid into alpha-L-iduronidase similar to those shown by normal control fibroblasts, despite having undetectable alpha-L-iduronidase enzyme activity. The maturation of alpha-L-iduronidase in fibroblasts from this patient was delayed compared with normal controls and showed accumulation of the 76 kDa intermediate, as well as the major 69 kDa, form of the enzyme.

The biosynthesis and maturation of N-acetylgalactosamine-4-sulphatase (4-sulphatase) was studied in normal fibroblasts and in fibroblasts from patients with either mucopolysaccharidosis type VI (MPS VI; Maroteaux-Lamy syndrome) or multiple sulphatase deficiency (MSD). Fibroblasts were incubated in culture medium containing [3H]leucine or [35S]methionine, and radiolabelled 4-sulphatase was isolated by immunoaffinity chromatography using 4-sulphatase-specific monoclonal antibodies. In normal fibroblasts a precursor of 66 kDa, detected intracellularly after 3 h and in NH4Cl-induced secretions, was processed intracellularly, within an additional 3 h, to a polypeptide of 57 kDa composed of disulphide-linked polypeptides of 43 kDa and 8 kDa. All fibroblast lines obtained from MPS VI patients, exhibiting clinical characteristics ranging from no clearly recognized symptoms to the severe classical phenotype, incorporated radioactivity into immune-purified 4-sulphatase at a rate less than 10% of that seen in normal fibroblasts. Maturation of the residual 4-sulphatase showed, variously, features which may be indicative of delayed intracellular transport, decreased intracellular stability, failure of lysosomal targetting or resistance to enzyme processing. Although some features of the residual enzyme synthesis and maturation were consistent with the patient's clinical phenotype, this was infrequent. The maturation of 4-sulphatase in fibroblasts from MSD patients was indistinguishable from that in normal fibroblasts, and the half-life of 4-sulphatase in these fibroblasts, determined after a 24 h pulse and prolonged chase, was only slightly less than that in normal fibroblasts.

A proteoglycan purified from 4 M-guanidinium chloride extracts of bovine periodontal ligament closely resembled that of bovine skin, except for a rather lower protein content and a higher molecular weight (120 000 compared with about 90 000) by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. The latter difference was explained by the molecular weights (29 000 and 16 000) of the respective dermatan sulphate components, each of which was rich in L-iduronate (about 75% of the total hexuronate). Significant amounts of other glycosaminoglycans did not occur in these proteoglycans, which were homogenous on gel chromatography and agarose/polyacrylamide-gel electrophoresis. Polydispersity was observed in sedimentation equilibrium experiments, but proteolysis or self-association of the proteodermatan sulphates may have affected these results. Ligament proteoglycans that were almost completely extracted with 0.1 M-NaCl contained less protein of a completely different amino acid composition than the proteodermatan sulphates. They were heterogeneous in size but generally smaller than cartilage proteoglycans and L-iduronate was a component, comprising about 7% of the total hexuronate of the sulphated galactosaminoglycan chains. The latter consisted of two fractions differing in molecular weight, but a dermatan sulphate with a high L-iduronate content was not present. These proteoglycans had some resemblance to D-glucuronate-rich proteoglycans of other non-cartilaginous tissues. Such compounds, however, are difficult to categorize at present.

Culture of chick-embryo sternal-cartilage chondrocytes within three-dimensional collagen gels promotes the synthesis of three low-molecular-weight collagenous polypeptides. The proportions of these novel collagens synthesized and released into the medium are markedly influenced by the presence or the absence of fibronectin in the serum supplement. Chondrocytes cultured on plastic dishes appear to synthesize only small amounts of these low-molecular-weight species. The three species (designated G, H and J) were characterized with respect to the proportion of [14C]proline incorporated into each polypeptide occurring as hydroxy[14C]proline and with respect to their susceptibilities to bacterial collagenase. On the basis of their electrophoretic mobilities under reducing conditions, the G, H and J polypeptides were calculated to have Mr 59 000, 69 000 and 84 000 respectively. Chymotrypsin digestion converted the G collagen into a species containing polypeptides of Mr 45 000, whereas the H and J polypeptides yielded a single band of Mr 53 000. The H and J polypeptides were found to occur as disulphide-linked aggregates, as was the chymotrypsin-digestion product. Peptide 'mapping' has shown that G, H and J polypeptides show no common identity and are distinct from the known interstitial collagens. Native G collagen was digested by human collagenase to discrete products, whereas H and J chains were not cleaved under identical conditions.

Initial purification of N-acetylgalactosamine-4-sulphate sulphatase from human liver homogenates containing approx. 1 mg of enzyme in 26 g of soluble proteins was achieved by a six-column chromatography procedure and yielded approx. 40 micrograms of a single major protein species. Enzyme thus prepared was used to produce N-acetylgalactosamine-4-sulphate sulphatase-specific monoclonal antibodies. The use of a monoclonal antibody linked to a solid support facilitated the purification of approx. 0.5 mg of N-acetylgalactosamine-4-sulphate sulphatase from a similar liver homogenate. Moreover the enzyme isolated contained a single protein species, shown by SDS/polyacrylamide-gel electrophoresis to have an Mr of 57,000, which dissociated into subunits of Mr 43,000 and 13,000 in the presence of reducing agents. Essentially identical enzyme preparations were isolated from homogenates of human kidney and lung and from concentrated human urine. The native protein Mr of enzyme from human liver and kidney was assessed by gel-permeation chromatography to be 43,000 on Ultrogel AcA and Bio-Gel P-150. The liver N-acetylgalactosamine-4-sulphate sulphatase was shown to have pH optima of approx. 4 and 5.5 with the oligosaccharide substrate (GalNAc4S-GlcA-GalitolNAc4S) and fluorogenic substrate (methylumbelliferyl sulphate) respectively. Km values of 60 microM and 4 mM and Vmax. values of 2 and 20 mumol/min per mg were determined with the oligosaccharide and fluorogenic substrates respectively.