For a malate dehydrogenase assay, samples (5 ml) of cultures in-
cubated for 25 h in the growth medium and for up to 35 h in the
production medium were prepared as previously described (Pines
et al. 1996).
For the determination of the kinetic parameters of MDH2, cells
harboring plasmid pGAL-MDH were broken by a French press (83
MPa) and centrifuged at 12 000 ´ g for 10 min at 4 oC. Protamine
sulfate (50 ll/ml 2% solution) was added to cell extracts, which
were then incubated for 15 min and centrifuged. To the superna-
tant fraction, solid ammonium sulfate was added to a ®nal con-
centration of 75%. The pellet obtained was suspended in 50%
ammonium sulfate solution and the suspension was centrifuged to
obtain the supernatant fraction, which was used for the MDH2
assay.
Saccharomyces cerevisiae DMM1-15A cells were grown for 9 h
in galactose medium labeled with [35S]methionine and cell extracts
were prepared as previously described (Pines et al. 1996; Stein et al.
1994).