Enzymatic assay of salicylate adapted to the Monarch centrifugal analyzer.

correlated well with those by the highly sensitive enzymatic method (x; the ACS-myokinase-lactate dehydrogenase method) used routinely. The regression equation was y = 1.lx-25.4, the correlation coefficient 0.99, showing excellent correlation. Normal concentrations of various kinds of anticoagulants, albumin, glucose, ascorbic acid, and hemo-globin had no effects on the results. In conclusion, the proposed chemiluminescent method for quantifying NEFA in serum showed high sensitivity, and the sample volume was smaller than that used in the colorimetric method. Inorganic pyrophosphate (PPi) has been measured in body fluids to examine its role in disorders of bone and cartilage, e.g., hypophosphatasia, chondrocalcinosis. That the concentration of PPi is higher in serum than in plasma has been attributed to release of PPi from the dense granules of platelets (1). In osteogenesisimperfecta, the concentration of PPi is increased in serum (2) but not in plasma (3). However, our data suggest that a fraction of the PPi measured in serum is derived from ATh which is also released from platelets. We are studying nucleoside triphosphate (NTP) pyrophos-phatase, which catalyzes the reaction: NTP-NMP + PPi. In examining whether this enzyme is present in body fluids, we used APP as substrate and measured the resulting PPi radiometrically (4). PPi was generated from APP in both serum and plasma, and the total measured activities in each were not significantly different (unpublished observations). However, in the absence of added APP, the concentration of PPi in serum increased (P <0.01, Student's paired t-test) from 6.30 ± 0.64 imoiJL to 8.52 ± 0.87 imol/L (mean ± SE, n = 6) afterincubation for 30 mm at 37 #{176}C. The mean concentration of PPi in plasma from the same individuals also increased slightly, but not significantly, from 2.75 ± 0.29 to 2.98 ± 0.33 pmoIfL.We suggest that the additional PPi in serum was generated by the action of NTP pyrophos-phatase on platelet-derived APP. The small increase in PPi in some plasma samples may also have been due to platelet-derived APP, because the use of a tourniquet can cause some platelet degranulation (5). These findings imply that ATP is catabolized during processing of serum. Indeed, we previously observed very high concentrations of PPi in sera that were processed only aftera lengthy delay (unpublished observations). Hence measurements of the concentration of PPi in serum should be interpreted with caution. It would be helpful to identify specific inhibitors of NW pyrophosphatase, which could be used to prevent …