INVOLVEMENT OF A MEMBRANE-BOUND FORM OF GLUTAMATE-DEHYDROGENASE IN THE ASSOCIATION OF LYSOSOMES TO MICROTUBULES

A 50-kDa membrane protein corresponding to a membrane-bound isoform of glutamate dehydrogenase was proposed as a molecular species that coul d mediate lysosome-microtubule interactions. This protein, isolated fr om purified lysosome membranes, is a peripheral membrane protein with an ATP-dependent microtubule binding activity, We have produced antibo dies against the purified 50-kDa protein to investigate its role in th e association of lysosomes to microtubules using a cell-free reconstit ution assay and cell microinjection, Pretreatment of purified lysosome s with the antibodies inhibited the association of these vesicles to m icrotubules. The blocking effect of antibodies was demonstrated by a d ifferential sedimentation method and negative staining electron micros copy, allowing us to quantify the amount of microtubules interacting w ith lysosomes and the proportion of lysosomes bound to microtubules, r espectively, Affinity-purified antibodies microinjected into intact ce lls altered the distribution of lysosomes that appeared less clustered in the vicinity of nuclei, The antibody-induced lysosome dispersion w as assessed by quantitative videomicroscope analyses. These data show that the 50-kDa membrane protein could act, through its microtubule bi nding activity, as a molecule of attachment of lysosomes to microtubul es. This membrane-bound isoform of glutamate dehydrogenase could be in volved in the microtubule-dependent perinuclear localization of lysoso mes.