[en] The mathematical and statistical theory of radioimmunoassays (RIAs) has been used to develop a series of computer programs to optimize sensitivity or precision at any desired dose level for either equilibrium or nonequilibrium assays. These computer programs provide for the calculation of the equilibrium constants of association and binding capacities for antisera (parameters of Scatchard plots), the association and dissociation rate constants, and prediction of optimum concentration of labeled ligand and antibody and optimum incubation times for the assay. This paper presents an experimental evaluation of the use of these computer programs applied to RIAs for human chorionic gonadotropin (hCG) and estradiol. The experimental results are in reasonable semiquantitative agreement with the predictions of the computer simulations (usually within a factor of two) and thus partially validate the use of computer techniques to optimize RIAs that are reasonably well behaved, as in the case of the hCG and estradiol RIAs. Further, these programs can provide insights into the nature of the RIA system, e.g., the general nature of the sensitivity and precision surfaces. This facilitates empirical optimization of conditions

[en] Previous work has indicated that heparan sulfate (HS) proteoglycans in rat ovarian granulosa cells are degraded by two kinetically distinct pathways. Pathway 1 degrades proteoglycans rapidly with a t 1/2 approximately 25 min without generating appreciable degradative intermediates. Pathway 2 degrades proteoglycans more slowly with a t 1/2 approximately 4 h, generating distinct degradative intermediates: single HS chains of Mr = approximately 10,000 and approximately 5,000. Effects of leupeptin, an inhibitor of thiol proteases, on the intracellular degradation of proteoglycans in the rat ovarian granulosa cell culture were examined using various chase protocols after labeling cells with [³⁵S]sulfate. The presence of leupeptin at 100 micrograms/ml in the culture medium inhibited the intracellular degradation of proteoglycans by approximately 80% during a 7-h chase period after a 20-h labeling. Leupeptin affected neither the cellular content nor the in vitro activities of beta-hexosaminidase and arylsulfatase. Structural analyses of heparan sulfate species in leupeptin-treated cells demonstrated that the drug inhibited the degradation of HS proteoglycans at two distinct points. First, degradation of the core protein was partially inhibited and delayed before the start of glycosaminoglycan degradation. This resulted in the accumulation of degradative intermediates with partially degraded core proteins bearing intact glycosaminoglycan chains. This establishes the initial sequence for HS proteoglycan degradation, with proteolysis preceding endoglycosidase digestion, and suggests that these two degradation steps may occur in physically separate compartments

[en] Murine monocytic leukemic (M1) cells were cultured in the presence of [³H]glucosamine and [³⁵S]sulfate. Labeled proteoglycans were purified by anion exchange chromatography and characterized by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis in combination with chemical and enzymatic degradation. M1 cells synthesize a single predominant species of proteoglycan which distributes almost equally between the cell and medium after 17 h labeling. The cell-associated proteoglycan has an overall size of about 135 kDa and contains three to five chondroitin sulfate chains (28-31 kDa each) attached to a chondroitinase-generated core protein of 28 kDa. The synthesis and subsequent secretion of this proteoglycan was enhanced 4-5-fold in cells induced to differentiate into macrophages. This was not a phenomenon of arrest in the G0/G1 stage of the cell cycle, since density inhibited undifferentiated cells arrested at this stage did not increase proteoglycan synthesis. The chondroitin sulfate chains contained exclusively chondroitin 4- and 6-sulfate; however, the ratio of these two disaccharides differed between the medium- and cell-associated proteoglycans, and changed during progression of the cells into a fully differentiated phenotype. Pulse-chase kinetics indicate the presence of two distinct pools of proteoglycan; one that is secreted very rapidly from the cell after a approximately 1-h lag, and a second pool that is turned over in the cell with a half-time of approximately 3.5 h. Subtle differences in the glycosylation patterns of the medium- and cell-associated species are consistent with synthesis of two pools. Papain digestion suggests that the chondroitin sulfate chains are clustered on a small protease resistant peptide. The data suggest that this proteoglycan is similar to the serglycin proteoglycan family

[en] The structure, biosynthesis, and distribution of cell-associated proteoglycans in a clonal line of parathyroid cells, which exhibit differentiated characteristics such as calcium-regulated hormone secretion and cell growth, were studied by metabolic labeling with [3H] glucosamine and [35S]sulfate as precursors. Proteoglycans were isolated by two consecutive ion exchange chromatography steps and then analyzed by gel filtration, polyacrylamide gel electrophoresis, and specific enzyme and chemical reactions. The cells synthesize almost exclusively (greater than 95%) heparan sulfate (HS) proteoglycans with a glycosaminoglycan synthesis rate of approximately 0.5 micrograms/10(6) cells/24 h. Two major HS proteoglycan species were identified. HS proteoglycan-I has a mass of approximately kDa with a single HS chain (approximately 12 kDa) and a core protein of approximately 150 kDa including oligosaccharides. HS proteoglycan-II has a mass of approximately 170 kDa with 3-4 HS chains (approximately 30 kDa) and a core protein of 70-80 kDa including oligosaccharides. In the medium with low ionized calcium (0.05 mM), HS proteoglycan-I is synthesized at approximately 1.6 times the rate and HS proteoglycan-II at a similar rate as for cells cultured in the medium with high ionized calcium (2.1 mM). The distribution of proteoglycans, examined by the accessibility of the molecules to trypsin, was dramatically influenced by environmental calcium concentration; at low calcium levels 70-80% of the HS proteoglycans are trypsin-accessible while only 20-30% are accessible at high calcium levels. This suggests that the proteoglycans are primarily on the cell surface in low calcium and in trypsin-inaccessible compartments in high calcium conditions

[en] Lowe (oculocerebrorenal) syndrome (LS) is an X-linked disorder characterized by congenital cataracts, generalized hypotonia, mental retardation, and renal Fanconi syndrome. The basic defect remains unknown, but the possibility that fibroblasts express reduced sulfation of glycosaminoglycans has been studied in several laboratories. A mechanism involving overproduction of an enzyme (nucleotide pyrophosphatase) active against adenosine 3'-phosphate, 5'-phosphosulfate (PAPS) has been postulated. Decreased synthesis of normally sulfated glycosaminoglycans was also reported. We measured the synthesis of proteoglycans and glycosaminoglycans by incorporation of [³H]glucosamine and Na₂(³⁵)SO₄ into cultured fibroblasts from four LS patients and related it directly to the synthesis in six normal fibroblast cultures. We found that the rate of synthesis varied greatly among the normal cultures (cv, 30%), but not significantly between LS and the normal. The LS fibroblasts' ability to sulfate glycosaminoglycans was assayed as the amount of ³H-glycosaminoglycan eluting at low ionic strength on anion exchange chromatography, the amount of non-sulfated disaccharide present in chondroitinase digests of labeled proteoglycans, and the ratio of ³⁵S to 3H incorporation into proteoglycans. Each parameter suggested that the LS cells were synthesizing normally sulfated glycosaminoglycans (e.g. % delta Di-0S, 21 +/- 6 in normal; 27 +/- 6 in LS). The cells' ability to sulfate glycosaminoglycans was tested under conditions of markedly stimulated glycosaminoglycan synthesis, by treating the cultures with a beta-D-xyloside

[en] The proteoglycans (cell-associated and culture media) in 3T3-L1 preadipocytes in culture were analyzed before and during differentiation into adipocytes. Cells were metabolically labeled with [35S]sulfate and [3H] glucosamine for 24 h and then extracted and analyzed. There was a 1.68 ± 0.07-fold increase in the 35S in medium proteoglycan during differentiation, whereas cell-associated proteoglycan radioactivity showed no increase. Analyses of radiolabeled molecules using ion-exchange chromatography, gel filtration, and high performance liquid chromatography after enzymatic or alkaline digestion indicated that all of the 35S label was recovered as two major species of chondroitin 4-sulfate proteoglycans (CSPG-I and CSPG-II) and 7% as heparan sulfate proteoglycan. CSPG-I has a mass of ∼ 970 kDa with multiple chondroitin sulfate chains (average of 50 kDa each) and a core protein of ∼ 370 kDa including oligosaccharides. CSPG-II has a mass of 140 kDa with one or two chondroitin sulfate chains (average of 68 kDa each) and a core protein of 41 kDa including oligosaccharides. CSPG-I appears to be similar to versican, whereas CSPG-II is similar to decorin and/or biglycan, found in other fibroblastic cells. Cell differentiation was associated with a specific increase in CSPG-I (4.0 ± 0.2-fold in media and 3.2 ± 0.5-fold in the cell-associated form). This system should facilitate study of the functional roles of proteoglycans during growth and differentiation