Evidence for the existence of mammalian acetoacetate decarboxylase: with special reference to human blood serum

Abstract

In this article evidence is presented for the existence of mammalian acetoacetate decarboxylase (acetoacetate carboxy-lyase: E.G. 4.1.1.4). From experiments with human blood serum the presence of a non-ultrafiltrable activator, accelerating the decomposition of acetoacetate into acetone and carbon dioxide, is established. Kinetic studies about this activator are performed by means of repeated gas Chromatographie determination of acetone in the head space vapour.

From the experiments with different, more or less purified, human protein fractions it can be concluded that the enzyme activity present in human blood serum is located in the albumin fraction and demonstrates : (1) an optimal activity at pH = 4.5, (2) a low substrate affinity (Km = 4 (± 1.5) · 10−1 M), (3) a temperature coefficient (Q10) of 2.5 in the range 20°–40°, (4) heat instability at 80°, (5) loss of activity by denaturation with HgCl2, (6) inhibition of enzyme activity by iodoacetate and urea, (7) activation of enzyme activity by lactoflavin. No inhibition of the enzyme activity was found by addition of CN− or pyruvic acid.

Also the presence of acetoacetate decarboxylase activity in rat liver tissue is mentioned.