An ELISA assay for GAP-43

An ELISA assay for the growth associated protein GAP-43 was developed to determine rapidly its relative abundance in neuronal tissue. The assay was performed with affinity-purified anti-GAP-43 antibody that detected a single band of M r = 42 000–45 000 on Western blots of rat brain homogenates but no bands on blots of liver homogenates. GAP-43 was determined by ELISA assay in as little as 0.6 μg protein of brain homogenate. The assay was highly reproducible; the standard error of the mean of sample to sample variation was less than 5%. When ELISA development time was held constant, the standard error of the mean of inter-assay variation was between 2 and 7%. Using this method, GAP-43 immunoreactivity was examined in developing rat brain. At post-natal day 1, GAP-43 immunoreactivity was 3–4 times greater than that observed in the adult, remained elevated for several weeks, and decreased by the end of the first month of life. These results are in accord with previous studies on the expression or synthesis of GAP-43 during neuronal development.