Betty E. Haskell

Effect of retinoic acid on nerve growth factor receptors

SummaryRetinoic acid (RA), a naturally occurring metabolite of vitamin A, increased the number of receptors for nerve growth factor (NGF) in cultured human neuroblastoma cells (LA-N-1), as indicated by an immunofluorescence assay of cell surface receptors and by specific binding of 125I-NGF to solubilized receptors. Analysis of 125I-NGF binding showed that RA increased the number of both high affinity and low affinity receptors for NGF without affecting the equilibrium dissociation constants. Neurite outgrowth similar to that produced by NGF occurred following RA-treatment in LA-N-1 cells, in the SY5Y subclone of SK-N-SH human neuroblastoma cells and in explanted chick dorsal root ganglia (DRG). Whether morphological changes following RA treatment are directly related to the increase in NGF receptors is unknown. Data presented here are consistent with literature reports that RA modifies cell surface glycoproteins, including those that act as cell surface receptors for epidermal growth factor and insulin.

An Improved Colorimetric Assay for Pyridoxal Phosphate Using Highly Purified Apotryptophanase

Methods for the analysis of pyridoxal phosphate, the principal cofactor form of vitamin B-6, have achieved new importance with the demonstration that levels of the coenzyme in serum constitute a useful test of vitamin B-6 nutritional status (1). Enzymic assays are among the most satisfactory for measuring pyridoxal phosphate in biological samples for several reasons: 1) they are highly specific, 2) they permit quantification of pyridoxal phosphate at the level of 10−11 moles, and 3) the analyses work well in crude biological extracts without prior isolation or purification.