We measured oxygen isotope ratios (delta18O) of xylem sap, phloem sap, leaves, wood and bark of Eucalyptus globulus Labill. growing in southwestern Australia. Carbon isotope ratios (delta13C) were measured in the dry matter of phloem sap, leaves and wood. Results were used to test several aspects of a mechanistic model of 18O enrichment and provided insights into post-photosynthetic variations ...

The aim of this study was to determine the kinetics of H(2)18O equilibration and elimination in preterm babies for the estimation of total body water. Thirteen, clinically stable, preterm babies of less than 32 weeks' gestation were studied in the first week after birth. Blood and urine samples were obtained for baseline measurement of 18O:16O ratio and 1 ml/kg of 10% H(2)18O (0.1 g/kg isotope)...

The first characterization of the kinetics and subcellular compartmentation of adenylate kinase activity in intact muscle has been accomplished using rat diaphragm equilibrated with [18O]water. Rates of adenylate kinase-catalyzed phosphoryl transfer were measured by appearance of 18O-labeled beta-phosphoryls in ADP and ATP resulting from the transfer to AMP of newly synthesized 18O-labeled gamm...

Pancreatic carboxylester lipase catalyzes the exchange of 18O between water and 13,16-cis,cis-doco-sadienoic acid (DA) in monolayers at the argon-buffer interface (Muderhwa, J.M., Schmid, P.C., and Brockman, H.L. (1992) Biochemistry 31, 141). In mixed monolayers of 18O, 18O-DA and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), both the extent and mechanism of 18O exchange show charact...

Irradiation of a Ne matrix sample containing NO and CO near 4 K with an ArF excimer laser at 193 nm yielded new lines at 2045.1 and 968.0 cm(-1) that were depleted upon secondary photolysis at 308 nm. These lines are assigned to C=O stretching and mixed stretching modes of ONCO, based on results of 15N-, 13C-, and 18O-isotopic experiments and quantum-chemical calculations. These calculations us...