Adenine phosphoribosyltransferase in patients with disorders of purine and pyrimidine metabolism.

Elevated levels of APRT activity are found in erythrocytes from most patients with a primary deficiency of HPRT. A twofold elevation of APRT activity has also been measured in hemolysate from one patient with a deficiency of both OPRT and ODC activity. In an attempt to further define the mechanisms responsible for these apparent alterations in APRT expression, we have studied the catalytic, immunochemical, and electrophoretic properties of APRT in erythrocytes from patients with these inborn errors of purine and pyrimidine metabolism. We have found that the elevated activity of APRT in HPRT-deficient erythrocytes results from an increased amount of a catalytically normal APRT protein. Immunochemical and electrophoretic studies that this APRT protein is structurally normal. One patient with a deficiency of OPRT-ODC demonstrated a fourfold increase in APRT protein; this enzyme was catalytically less efficient than APRT from normal controls.