Cell Calcium (1987) 8. 229-239 t Lungman Group UK Ltd 1987 IDENTIFICATION OF BOVINE BRAIN CALCIUM BINDING PROTEINS Masaaki Tokuda, Navin C. Rhanna and David M. Waisman Cell Regulation Group, Department of Medical Biochemistry, The University of Calgary, Calgary, Alberta, Canada T2N 4Nl (reprint requests to DMW) ABSTRACT Three peaks of calcium binding activity have been identified by the Chelex-106 calcium binding assay of the fractions from DEAE cellulose chromatography of 100,000 x g supernatant of bovine brain. These calcium binding activity peaks have been subjected to extensive purification and three novel calcium binding proteins (Mr 27,000, Mr 48,000 and Mr 63,000) and two previously characterized proteins (calcineurin and calmodulin) have been identified as components of calcium binding activity peaks. Analysis of the calcium binding properties of the novel proteins by equilibrium dialysis suggests these proteins may be intracellular calcium receptors. INTRODUCTION Calcium is believed.to play a crucial role in the process of synaptic transmission. When an action potential arrives at a presynaptic nerve terminal the resultant membrane depolarization opens calcium channels in the presynaptic membrane. The resultant influx of calcium leads to a transient rise in the intracellular calcium concentration;this is believed to be the intracellular signal for neurotransmitter release (1). Electrophysiological and morphological studies have indicated that the calcium induced fusion of synaptic vesicles with the presyn- aptic membrane is a key event in the release process (2). Changes in cytoplasmic calcium have multiple consequences on synaptic function. Nerve terminal glycogenolysis and respiration are increased in response to the calcium signal (3). Cytoplasmic calcium also stimulates the synthesis of several neurotransmitters by increasing the activity of rate limiting transporters of enzymes. For example, choline transport in cholinergic neurons, and tyrosine hydroxylase in catecholamine neurons are activated by increases in cytoplasmic calcium. Cytoplasmic calcium also reduces the activity of certain calcium channels and activates calcium dependent potassium channels resulting in changes in synaptic efficiency (reviewed in 2). 229