ENZYMES (ISOENZYME SYSTEM) AS HOMEOSTATIC MECHANISMS THE ISOENZYME (ADA2) OF ADENOSINE-DEAMINASE OF HUMAN MONOCYTES-MACROPHAGES AS A REGULATOR OF THE 2'DEOXYADENOSINE

Regarding homeostatic mechanisms in the enzyme (isoenzymes) and substr ate system we show through a simulation model obtained by STELLA II so ftware that: (i) a pair of isoenzymes (Is1 and Is2) that have differen t affinity far the substrate (Is2 affinity < Is1 affinity), can consti tute an efficient homeostatic mechanism: by varying the relative conce ntration of the isoenzymes in the system, the levels of the substrate can be controlled; (ii) the isoenzymes ADA1 and ADA2 of adenosine deam inase (ADA) that have different affinity for the substrate 2'deoxyaden osine (ADA2 has very weak affinity for 2'deoxyadenosine) constitute, i nside human Monocytes-Macrophages, a homeostatic mechanism that assure s an up-regulation of 2'deoxyadenosine and a down-regulation of a seco nd substrate (adenosine) for which the affinity of the two isoenzymes is similar.