[Microassay of adenine by an enzymatic isotope dilution kinetics method]

Owing to the very low levels of adenine in the intracellular and extracellular compartments and its low excretion by the kidney, no method of estimation was, until now, sufficiently specific and sensitive to determine precisely quantities of the order of 1 nanomole. The method of "isotopic enzymatic kinetic dilution" proposed by Newsholme et Taylor, has been used. The kinetic conditions of the reaction catalysed by adenine-phosphoribosyltransferase are favourable, [in particular KM (adenine) is very low, about 2.1(-6) M] and are not very sensitive to the action of other effectors. The technique proposed permits one to determine quantities of adenine between 0.05 and 1.2 nmole, i.e. 0.007 to 0.16 mug, with a precision of about 5 p. cent. Easy to carry out, it is useful in large series. Normal values in man of adenine thus measured (15 adult subjects) were as follows: Plasma: 1.13 +/- 0.41 nmoles.ml(-1), i.e. 0.152 +/-0 0.055 mug.ml(-1). Red cells: 3.65 +/- 0.87 nmoles.ml(-1), i.e. 0.493 +/- 0.117 mug.ml(-1). Urine (24 hour excretion): 11.41 +/- 1.24 mumoles, i.e. 1.54 +/- 0.17 mg.