The synthesis and subcellular distribution of pyridoxal phosphate in rat and bovine retinas

In the absence of any known studies dealing with status of vitamin B₆ metabolism in mammalian retinas, the concentration of pyridoxal phosphate and the activity of its synthesizing enzyme pyridoxal kinase were determined in rat retina and bovine retina and its subcellular compartments. In bovine retina, the highest concentration of pyridoxal phosphate (148 pmol/mg protein) was present in pellet 2 fraction containing synaptosomes comparable to those isolated from brain. The second highest concentration of pyridoxal phosphate (91 pmol/mg protein) was present in pellet 1 fraction containing large synaptosomes resembling photoreceptor cell terminals. The concentrations of pyridoxal phosphate in pellets 1 and 2 fractions were approx 3- to 6-fold higher than that found in the whole retina. The concentration of pyridoxal phosphate and the activity of pyridoxal kinase in the rat retina were considerably higher than those observed in the bovine retina. In general, no apparent correlation existed between the concentrations of pyridoxal phosphate and the activities of pyridoxal kinase in bovine retina and its subcellular compartments.