Significance of adenosine deaminase activity and its isoenzymes in tuberculous effusions.

Adenosine deaminase (ADA) activity is increased in effusions caused by certain clinical conditions including tuberculosis and bacterial infections. In this study, the ADA isoenzyme patterns in tuberculous and parainfective effusions were investigated to determine the isoenzyme responsible for this increase in activity. Fifty-one tuberculous effusions and six parainfective effusions were investigated. All effusions had increased ADA activity (median values of 126 and 127 units/L, respectively). In the tuberculous effusions, ADA2 isoenzyme was found to be primarily responsible for total activity, with a median contribution of 88 percent. The ADA1 (both ADA1m and ADA1c isoenzymes) was the major isoenzyme in the parainfective effusions with a median contribution of 70 percent. The ADA2 isoenzyme activity most likely reflects monocyte-macrophage turnover or activity, while ADA1 probably originates from lymphocytes or neutrophils. It is therefore essential to determine the isoenzyme profile when interpreting ADA activity levels in effusions. The measurement of the individual isoenzymes will enhance the diagnostic utility of ADA activity determinations in pleural effusions.

An enzymatic assay of inorganic phosphate in serum using nucleoside phosphorylase and xanthine oxidase.

We have developed a new enzymatic assay for the determination of inorganic phosphate (Pi) in serum, using nucleoside phosphorylase (NP) and xanthine oxidase (XOD). Pi and inosine react to form hypoxanthine and ribose-1-phosphate. The hypoxanthine is oxidized to xanthine, which is further oxidized to uric acid. In these two reactions 2,6-dichlorophenol-indophenol (DCIP) is reduced to a colourless compound and the decrease in colour is measured spectrophotometrically at 600 nm. The assay is automated with an RA-XT analyser. The precision of the automated assay is acceptable (C.V. < 3.5%) and results are accurate and linear across a range of values from 0.2-2.5 mmol/l. The assay correlates well with molybdate methods carried out on SMAC III and RA-XT analysers (r values 0.99 and 0.98, respectively), and seems to be less prone to non-specific sample interference than the usual RA-XT method. The enzymatic assay described seems to be suitable for the routine determination of serum Pi.

Kinetic determination of serum adenosine deaminase.

A new kinetic method for the determination of serum adenosine deaminase (EC 3.5.4.4) is described, with adenosine as the substrate and nucleoside phosphorylase and xanthine oxidase as the reaction enzymes. Inosine is produced, which is converted to hypoxanthine. The hypoxanthine is oxidized to xanthine, which is further oxidized to uric acid. In these two reactions, blue 2,6-dichlorophenolindophenol is reduced to a colorless compound and the decrease in color is measured spectrophotometrically at 606 nm. The assay was automated by using a Cobas Mira analyzer. The automated assay had a CV of < 7%, and the calibration curve was linear from 10 to 120 U/L. The assay correlates well with an established method, based on detection of liberated NH3 with Berthelot's reaction. The reference interval (mean +/- 2 SD) was 14-34 U/L (mean 24 U/L, n = 84). The enzymatic method described is easily automated and seems to be suitable for the routine determination of adenosine deaminase in serum.

Serum adenosine deaminase: isoenzymes and diagnostic application.

Human adenosine deaminase (ADA; EC 3.5.4.4) consists of three isoenzymes: ADA1, ADA1+CP, and ADA2. We developed an electrophoretic technique to distinguish between these three isoenzymes. The isoenzyme pattern was studied in tissue and cell homogenates, as well as in serum from normal subjects and from patients with increased serum ADA who had either hepatitis, infectious mononucleosis, tuberculosis, pneumonia, rheumatoid arthritis, or acute lymphoblastic leukemia (ALL). The highest ADA activity was found in lymphocytes and monocytes. ADA2 could be detected only in monocytes (18% of total ADA activity). It was also the predominant isoenzyme in the sera of controls and all disease groups, except for ALL--the only condition evaluated that is not of an inflammatory nature. We conclude that serum ADA reflects monocyte/macrophage activity or turnover in most diseases studied. The exception is ALL, where serum ADA most probably originates from lymphocyte precursors.