Brain content of cobalamin and its binders in elderly subjects

The biological aspects of cobalamin were studied in autopsy brains of eight elderly subjects who had lacked marked neurologic symptoms. Separation of the gray and white matter of the frontal and temporal lobes, and subsequently, subcellular fractionation of each matter were attempted. The contents of cobalamin and its binders and cobalamin concentrations were measured in each subcellular fraction and whole homogenate. The contents of cobalamin were in the ranges of 50 to 60 ng/g wet tissue. No marked differences in contents were found between the frontal and temporal lobes. The mitochondria-rich fraction contained more cobalamin than did the microsomal fraction. Two binders were found; a large-sized and a small-sized. The molecular weight of the larger binder was ca. 120,000, coinciding with the elution region of transcobalamin I, and the molecular weight of the smaller binder was 40,000, coinciding with the elution region of transcobalamin II, in gel filtration respectively. More of the larger binder than the smaller was found in the mitochondria-rich and microsomal fractions. These data are useful for the study of various aspects of cobalamin in brains with various types of neurologic pathology or aging changes.