Albumin possesses intrinsic enolase activity towards dihydrotestosterone which can differentiate benign from malignant breast tumors.

Serum albumin was found to possess enolase activity towards the dihydrotestesterone (DHT) molecule, converting it from its 3-keto to 3-enol form. This activity was accompanied by albumin during all stages of purification, as well as following various treatments, a fact indicating that the enzymatic activity was an intrinsic property of albumin molecule and did not represent an impurity of the preparation. Enolase activity was decreased in parallel with the quantity of intact albumin molecules when proteolytic enzymes were used for their degradation. The activity was strongly inhibited by Ni (II) and Cu (II) ions, which bind to 3-histidine of the albumin molecule, as well as by oleic acid and cholesterol. It was also inhibited, in a reversible manner by surface-active agents. Enolase activity was found in all mammalian species studied, the specific activity however was very low in the serum of dogs. The administration of DHT to mice did not influence the albumin or enolase levels in their serum. The optimum pH of enolase was at 9.2, with a carbonate buffer solution. In addition to the serum enolase activity was found to be a feature of intracellular albumin. The two albumins exhibited the same specific activity and the same Km for DHT. The study of cytosolic albumin, obtained from human mammary gland tissue, revealed that benign and malignant tumors of this gland differed substantially with respect to their percentage of albumin. Significant differences were also observed in enolase activity, a consequence of the existence of a fraction of albumin in the malignant tissue in a polymeric form. This form exhibited a decreased enzymatic activity, compared to its monomeric form, exclusively encountered in benign breast specimens. The last observation, along with the quantitative differences of albumin in the two tissues, offers a possibility of reliable differentiation between benign and malignant breast tumors.