Estudio comparativo del comportamiento cinético de mutantes de Mycobaterium sp. en la biotransformación de esteriodes.

The enzyme steroid 1,2 dehydrogenase in microorganisms degrading sterols catalyzes the formation of androstadien-3,17-dione (ADD) from 4-androsten-3,17-dione (AD). The reaction introduces a double bound at the 1,2 position in ring A of the steroidal nucleus. This paper shows the results of the kinetic study of this enzyme in strains Mycobacterium sp. NRRL-B3683 and Ex4, a derived mutant from the former. Both strains are ADD producers as the main phenotype. Determination of the kinetic parameters includes the Michaelis-Menten constant (Km), the maximal velocity of the enzymatic reaction (Vmax), optimal temperature and pH, as well as its thermostability. Maximal activity was achieved at 25 °C, and pH values from 7,8 to 8,8. On the other hand, Km and Vmax were 4 . 10-4 M and 20 nmol/mL, respectively. The above results are compared to biotransformation behavior of the strains in fermentation experiments having cholesterol, stigmasterol and a phytosterol mixture from sugar cane oil as substrates. ADD yield was similar when cholesterol was used as substrate in both strains. However, the AD/ADD ratio was smaller in Ex4, so that this strain must harbor a higher steroid 1,2 dehydrogenase activity. [ABSTRACT FROM AUTHOR]