Biomedical subjects
Publications and source records attributed to I R Dickson.
In chick bone collagen the degree of lysine hydroxylation and the magnitude of the crosslink ratio dihydroxylysinonorleucine/hydroxylysinonorleucine were both found to be inversely related to the concentration of plasma calcium. Lysine hydroxylation was also affected by a second factor related to vitamin D status.
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1. The process of diaphyseal bone formation can be investigated by studying the rate of incorporation of radioactive precursors, administered in vivo into bone fractions of increasing density. 2. In the 4-week-old vitamin D-treated chick most of the osteoid becomes calcified within 12h and almost all within 2 days. The low-density calcified phase that is formed is converted into a higher density form and within 7 days the greater proportion of the calcified tissue is in the higher density form. 3. In the vitamin D-deficient chick of similar age the rate of calcification of osteoid is decreased, as is the rate of conversion into the higher density phase with the resultant accumulation of the lower density calcified form. 4. The higher density phase probably corresponds to hydroxyapatite and the lower density one to the ACP-pase described by Termine & Posner [(1967) Calcif. Tissue Res. 1, 8--23]. 5. The disorder in the process of calcification seems to be unrelated to the alteration in blood Ca2+ and phosphate concentrations, but related to the presence or absence of cholecalciferol.
1. Proteoglycan was isolated from growth cartilage of normal and rachitic chicks. 2. The proteoglycan from normal cartilage showed differences in chemical composition and physical properties from a comparable fraction isolated from bovine nasal cartilage. 3. The proteoglycan from rachitic-chick cartilage was of smaller size than tis normal counterpart, though of similar average chemical composition. 4. Differences between proteoglycan from normal and rachitic cartilages can be explained in terms of limited proteolytic cleavage.
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The phosphoprotein obtained by the neutral pH tris buffer extraction of acetic acid demineralized bovine dentin has been compared with the phosphoprotein extracted directly during the neutral pH EDTA demineralization process. The phosphoproteins isolated by DEAE-cellulose chromatography from the neutral pH EDTA demineralization extract are not identical to those isolated by the same procedure from the dentin which had been subjected to acid demineralization. The two demineralization procedures yield phosphoproteins different in amino acid content and in presence of 260 nm UV absorbing moiety. Even after sequential acid demineralization, trisbuffer extraction and EDTA extraction, the residual dentin contains phosphoprotein. A peptide fragment containing both collagen and phosphoprotein moieties has been isolated following digestion and cleavage of the insoluble dentin collagen with cyanogen bromide. The acid demineralization process appears to be accompanied by degradation which removes both protein and non-protein components from the phosphoprotein.
Immunological and biochemical techniques demonstrated that the non-collagenous proteins of the organic matrix of bone were abnormal in quantity and composition in four children with osteogenesis imperfecta. This represents the main molecular difference found so far between bone in osteogenesis imperfecta and normal bone.
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