Intermediate Filaments in Nervous Tissues a Similar Preparation from Rabbit Brain Shows Four Major Polypeptides with Mol

In t e rmed ia t e f i laments have been isola ted from rabbi t in t radura l spinal nerve roots by the axonal f lo ta t ion me thod . This m e t h o d was modi f ied to avoid exposure of axons to low ionic s t rength me d ium. The pur i f ied f i laments are morpho log ica l ly 7 5 8 0 % pure . The gel e l ec t ropho re tog ram shows four m a j o r bands migra t ing at 200 ,000 , 145,000, 68 ,000, and 60 ,000 dal tons , respect ively . A similar p repa ra t ion from rabbi t brain shows four ma jo r po lypep t ides with mol wt of 200 ,000 , 145,000, 68 ,000 , and 51 ,000 dal tons . These results indicate that the neuro f i l amen t is c o m p o s e d of a t r iplet of po lypep t ides with mol wt of 200 ,000 , 145,000, and 68 ,000 dal tons . The 51 ,000-da l ton band that appea r s in brain f i lament p repa ra t ions as the ma jo r po lypep t ide seems to be of glial origin. The significance of the 60 ,000-da l ton band in the nerve root f i lament p repa ra t ion is unclear at this t ime. A n t ibod i e s ra ised against two of the tr iplet p ro te ins isola ted from calf brain localize by immunof luorescence to neurons in centra l and pe r iphera l nerve . On the o the r hand, an an t ibody to the 51 ,000-da l ton polypep t ide gives only glial s taining in the bra in , and very weak pe r iphera l nerve staining. P ro longed exposure of axons to low ionic s t rength med ium solubil izes a lmost all of the t r iple t po lypep t ides , leaving behind only the 51 ,000-da l ton c o m p o n e n t . This would indicate that the neurof i l ament is soluble at low ionic s t rength, whereas the glial f i lament is not . These results indicate that neurof i l aments and glial f i laments are c o m p o s e d of different po lypep t ides and have different solubil i ty character is t ics .