Adsorption of Nerve Growth Factor onto Surfaces Implications for the Assay in Tissue Culture

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Abstract
Apparently minor modifications to the basic method for the assay of nerve growth factor resulted in differences in measured biological activity of up to nine orders of magnitude. These differences were caused by the reversible adsorption of the material onto the apparatus used in the assay procedure. The adsorption was probably promoted by London dispersion forces since the effect persisted both over a range of pH and when glass, plastic and silicone‐coated glass apparatus were used.Under conditions in which the adsorption was minimised, the test material showed a specific activity in tissue culture of between 10−2 and 10−3 [μg ml−1. Previous reports of highly active preparations of nerve growth factor, some having specific activities of about 10−10μg ml−1, can probably be attributed to similar artefacts in the assay method.