Glycosaminogycans (GAGs) are involved in numerous vital functions in the human body. Mapping the GAG concentration in vivo is desirable for the diagnosis and monitoring of a number of diseases such as osteoarthritis, which affects millions of individuals. GAG loss in cartilage is typically an initiating event in osteoarthritis. Another widespread pathology related to GAG is intervertebral disk degeneration. Currently existing techniques for GAG monitoring, such as delayed gadolinium-enhanced MRI contrast (dGEMRIC), T1, and 23 Na MRI, have some practical limitations. We show that by exploiting the exchangeable protons of GAG one may directly measure the localized GAG concentration in vivo with high sensitivity and therefore obtain a powerful diagnostic MRI method.cartilage ͉ MRI ͉ osteoarthritis ͉ NOE ͉ proteoglycan

ly. The oxygen fugacity (/02) of the experiments was not buffered externally. However, /02 calculations based on biotite-sanidine-magnetite-H20-02 equilibrium [D. R. Wones, Kozan Chishitsu 31, 191 (1981)] yield /02 values 1.5 to 2 log units above the nickel-nickel oxide buffer. This is consistent with the estimated f02 conditions of natural epidote-bearing magmas {6, 16). Quenched experimental charges were sectioned longitudinally, polished, and examined with reflected-light microscopy and backscattered electron imaging. Rim widths were measured with an optical microscope equipped with a graduated ocular lens; the rim widths reported are the average of 20 to 30 measurements. Rim width data are as follows: experiment Ep-10, t = 51.17 hours, rim width = 2.74 ± 0.9 fjim; experiment Ep-12, t = 141.20 hours, rim width = 4.95 ± 0.8 fjtm; and experiment Ep-11, t = 378.78 hours, rim width = 8.18 £ 1.3 fjtm. 9. D. C. Rubie and A.

High-resolution phosphorus-31 nuclear magnetic resonance (31P NMR) spectra of wild-type and mutant strains of Saccharomyces cerevisiae were observed at a frequency of 145.7 MHz. Levels of various phosphorus metabolites were investigated upon addition of glucose under both aerobic and anaerobic conditions. Three mutant strains were isolated and their biochemical defects characterized: pfk lacked phosphofructokinase activity; pgi lacked phosphoglucose isomerase activity; and cif had no glucose catabolite repression of the fructose bisphosphatase activity. Each mutant strain was found to accumulate characteristic sugar phosphates when glucose was added to the cell suspension. In the case of the phosphofructokinase deficient mutant, the appearance of a pentose shunt metabolite was observed. 31P NMR peak assignments were made by a pH titration of the acid extract of the cells. Separate signals for terminal, penultimate, and central phosphorus atoms in intracellular polyphosphates allowed the estimation of their average molecular weight. Signals for glycero(3)phosphochline, glycero(3)phosphoserine, and glycero(3) phosphoethanolamine as well as three types of nucleotide diphosphate sugars could be observed. The intracellular pH in resting and anaerobic cells was in the range 6.5--6.8 and the level of adenosine 5'-triphosphate (ATP) low. Upon introduction of oxygen, the ATP level increased considerably and the intracellular pH reached a value of pH 7.2--7.3, irrespective of the external medium pH, indicating active proton transport in these cells. A new peak representing the inorganic phosphate of one of the cellular organelles, whose pH differed from the cytoplasmic pH, could be detected under appropriate conditions.