[Giardia duodenalis: analysis of malic enzyme expression with isoelectric focusing]

We wish to propose a data base of the isoelectric point (pl) for Giardia duodenalis isozymes [corrected]. As a contribution to this end we characterized by electrophoresis the isozymes of the malic enzyme (ME) of ten G. duodenalis isolates from Mexican children. Isoelectric focusing was performed in a vertical system using a one mm slab gel of 5.5% acrylamide prepared with 6.5% carrier ampholytes, pH 3-10, and 10% glycerol. Each test sample (10 micrograms) and a series of protein markers of known pl were applied in duplicate, and a minimum of six samples for each isolate were prefocused at 1.5 W, 200 V for 0.25 hour and focused at 2100 volt-hour, 3 W, 800 V. With the regression equation for protein markers Y = 1.886 + 5.709(X) (standard error for X = 0.001 and Y = 0.136), we calculated the pls for each isozyme of the malic enzyme detected in the G. duodenalis isolates. The pl of the isozymes were between 5.70-7.63 and the clone INP-100588-CMG1 was different from the parental isolates in three isozymes: pl 7.34, 7.16 and 6.99. The determination of isoelectric points of the isozymes of other enzymes of Giardia duodenalis should be a useful tool for the detection of their genetic variability by numeric comparison.