1987 Volume 15 Issue 5 Pages 285-291
We developed a kinetic method for measuring the activities of adenosine deaminase (EC 3.5.4.4, adenosine aminohydrolase: ADA) isozymes, based on their different Km values for adenosine as substrate. ADA activity was measured using two different concentrations of substrate; high (20 mmol/l) and low (0.5 mmol/l) concentration solutions of adenosine.
This kinetic method dose not require gel filtration, and is thus a relatively simple and rapid procedure.
Serum ADA is separated by gel filtration into two types of isozymes which have been called ADAi (small form; 35,000 daltons and large form; 280,000 daltons) and ADA2 (intermediate form; 100,000 daltons). ADA2 shows markedly different kinetic properties from those of ADA1; ADA2 has a higher Km value for adenosine and a lower deamination activity for 2'-deoxyadenosine than ADA1.
Analytical recoveries of ADA isozymes by the kinetic method varied from 93.3 to 116.3%. Results of the present method correlated well with those of the gel filtration method in high-performance liquid chromatography.
In clinical application, increased serum ADA2 activity was observed in chronic liver diseases, such as chronic hepatitis, liver cirrhosis, and hepato-celluler carcinoma. However, serum ADA1 activity did not increase significantly in only a few of many cases chronic liver disease. Studies on serial measurements of serum ADA isozymes in patients with liver disorders have demonstrated that the changes of ADA1 activity are similar to those of aspartate aminotransferase and alanine aminotransferase activity, but the changes of ADA2 activity differ.
These results suggest that measurement of serum ADA isozymes activities by the present method is useful for testing liver function.
