Enrichment of bacteriorhodopsin with isotopically labeled amino acids by biosynthetic incorporation in Halobacterium halobium

Abstract

The growth of Halobacterium halobium was optimized in a chemically defined synthetic medium. Arginine, isoleucine, leucine, lysine, methionine, tyrosine, and valine were found to be essential for growth. Optimal growth rates and cell yields were obtained when the medium was also supplemented with the nonessential amino acids alanine, asparagine, glutamic acid, glycine, phenylalanine, proline, serine, and threonine. The complete synthetic medium supported the same maximum growth rate, cell yield, and production of the integral membrane protein bacteriorhodopsin as was obtained in a complex peptone-based growth medium. Using this defined synthetic medium, isotopically labeled bacteriorhodopsin was produced with several 13C-enriched amino acids. The yield of 13C-labeled bacteriorhodopsin was greater than 35 milligrams of purified protein per litre of cell culture. Key words: bacteriorhodopsin, biosynthetic isotopic labeling, synthetic culture medium, nuclear magnetic resonance.