To demonstrate that the lipid volume fraction in liver steatosis can be accurately estimated with in vivo hydrogen-1 magnetic resonance (MR) spectroscopy, the authors developed a calibration procedure based on in vitro MR spectroscopy of lipid extracts from steatotic liver specimens. The lipid volume fractions determined with the calibration procedure were compared with the results of histomorphometry and with calibrated computed tomographic (CT) data. The volume fraction of fat determined with MR spectroscopy was in good agreement with the CT results, whereas histomorphometry underestimated the amount of hepatic fat. The results indicate that determination of the fat volume fraction in steatotic liver can be achieved noninvasively with MR spectroscopy.

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A glycoprotein that exhibits alkaline phosphatase activity and binds Ca2+ with high affinity has been extracted and purified from cartilage matrix vesicles by fast protein liquid chromatography. Antibodies against this glycoprotein were used to analyze its distribution in chondrocytes and in the matrix of calcifying cartilage. Under the light microscope, using immunoperoxidase or immunofluorescence techniques, the glycoprotein is localized in chondrocytes of the resting zone. At this level, the extracellular matrix does not show any reaction. In the cartilage plate, between the proliferating and the hypertrophic region, a weak immune reactivity is seen in the cytoplasm, whereas in the intercolumnar matrix the collagen fibers appear clearly stained. Stained granular structures, distributed with a pattern similar to that of matrix vesicles, are also visible. Calcified matrix is the most stained area. These results were confirmed under the electron microscope using both immunoperoxidase and protein A-gold techniques. In parallel studies, enzyme activity was also analyzed by histochemical methods. Whereas resting cartilage, the intercellular matrix of the resting zone, and calcified matrix do not exhibit any enzyme activity, the zones of maturing and hypertrophic chondrocytes are highly reactive. Some weak reactivity is also shown by chondrocytes of the resting zone. The observation that this glycoprotein (which binds Ca2+ and has alkaline phosphatase activity) is synthesized in chondrocytes and is exported to the extracellular matrix at the time when calcification begins, suggests that it plays a specific role in the process of calcification.

Rat incisor dentine was demineralized and extracted with 0.25 M EDTA containing protease inhibitors. The extract was purified by chromatography on DEAE-cellulose and sulfonated polystyrene. The Ca2+-binding properties of the phosphoprotein were studied by dynamic dialysis and by using a Ca2 +-selective electrode. Two different binding sites were detected with & = 0.9 x 10-M and 1.1 x lo-' M and displaying a Ca2+-binding capacity of 127 and 176mol bound Ca2+/mol protein, respectively, assuming a molecular weight of 30 000. Upon enzymatic dephosphorylation of the phosphoprotein, the highest affinity sites disappeared and those with the lowest affinity were reduced. The optimum for Ca2+ binding by the phosphoprotein occurred at pH 8.2. The specificity of the Ca2+ ion interaction with the phosphoprotein was investigated by studying the competitive nature of other divalent and monovalent cations. It was found that Ca2 + ions were to a large extent displaced from the phosphoprotein by other cations in physiological concentrations.Non-collagenous proteins present in the extracellular matrix may play an important role in the formation of calcium phosphate mineral in the collagenous network of bone and dentine.The presence of phosphoprotein in bovine dentine was first suggested by Veis and Schlueter [l-], and thereafter much effort has been put into studies of this type of proteins in calcified tissues from different species [2, 31. These molecules are strongly polyanionic due to an abundance of phosphate and carboxyl groups. In rat incisor dentine the phosphoprotein is the major non-collagenous protein present [4], and it has a peculiar amino acid composition in that half of the residues are serine (including phosphoserine) and one third is aspartate [4, 51. The interaction between the collagenous network and the phosphoprotein has not been completely elucidated, though it has been suggested that a minor part of the total phosphoprotein in dentine is covalently bound to the collagen [6], while the major, residual part would be bound through electrostatic forces.In view of its structure, the phosphoprotein could be expected to have a certain affinity for cations such as Ca2+. Bone and dentine formation has been suggested to involve a nucleation mechanism that is instrumental in the deposition of calcium phosphate in the organic matrix, possibly simultaneously with some chemical modifications of the latter [7]. The probable involvement of the non-collagenous phosphoprotein in the ~-Enzyme. Alkaline phosphatase (EC 3.1.3.1). development of minerals of dentine by facilitating the formation of a mineral phase is supported by the rapid appearance of serine and phosphate at the mineralization front, but not in predentine of rat incisor following intravenous injection [8]. This finding is consistent with the fact that the phosphoprotein is present in mineralized dentine but not in predentine [9] (and M. Jontell and A. Linde, unpublished). The effect of dental phosphoprotein on mineral formation is also shown by its ability to...

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