It was previously shown that a single amino acid substitution in the glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH) resulted in increased association of that enzyme with microtubules. This mutant GAPDH was discovered in a CHO cell exhibiting altered endocytosis. It has now been shown that transfection of wild-type CHO cells with GAPDH cDNA containing this mutation results in these same changes in endocytic activity; based on steady-state RNA levels about 15% of the total GAPDH in the stable transfectants contains the amino acid substitution. The principal effect of the mutant GAPDH on endocytosis appears to be increased microtubule-dependent centrifugal movement of late endocytic compartments (late endosomes and lysosomes). The mechanisms underlying the action of this mutant enzyme, as well as of other mutant forms of GAPDH generated in vitro, are currently under investigation.
