Investigations of the band shapes in absorption spectra of 3-hydropyridine derivatives, Schiff bases, enzymes containing pyridoxal phosphate and visual pigments will be continued. Spectra will be fitted with lognormal distribution curves and microscopic dissociation constants will be estimated. Various analogs of pyridoxal phosphate modified in the 5-position will be prepared through the use of 5'-deoxy-5-bromopyridoxal. Various studies of crystalline aspartate aminotransferase will be conducted. We will prepare large crystals of the enzyme-substrate and enzyme-inhibitor complexes for diffraction studies of optical spectra. We will systematically investigate conditions for crystallization and will compare the properties of a variety of complexes with anions. We will prepare a series of mercury-labeled derivatives for x-ray crystallography. Characterization of the product formed by reaction of serine sulfate and glutamate decarboxylase will be completed. We will attempt to synthesize the compound from 5'-bromo-5'-deoxypyridoxal. Efforts to devise a new affinity column for aspartate-dependent enzymes will be continued. In addition, the reaction of the substrate 2-hydroxymethylaspartate with aspartate aminotransferase will be investigated. BIBLIOGRAPHIC REFERENCES: Reaction of Glutamate Decarboxylase with Serine Sulfate. John J. Likos and David E. Metzler, Federation Proceedings 35, 1545 (1976) Abstract. Quantitative Description of Absorption Spectra of Schiff Bases Derived from Pyridoxal Phosphate. David E. Metzler, Allen Cahill, Carol M. Harris, John Likos and Bob Yang, Federation Proceedings 36, 855 (1977) Abstract.