1. Expanding the genetic code of Escherichia coli
L Wang, A Brock, B Herberich, P G Schultz Science. 2001 Apr 20;292(5516):498-500. doi: 10.1126/science.1060077.
A unique transfer RNA (tRNA)/aminoacyl-tRNA synthetase pair has been generated that expands the number of genetically encoded amino acids in Escherichia coli. When introduced into E. coli, this pair leads to the in vivo incorporation of the synthetic amino acid O-methyl-l-tyrosine into protein in response to an amber nonsense codon. The fidelity of translation is greater than 99%, as determined by analysis of dihydrofolate reductase containing the unnatural amino acid. This approach should provide a general method for increasing the genetic repertoire of living cells to include a variety of amino acids with novel structural, chemical, and physical properties not found in the common 20 amino acids.
2. Preclinical and clinical evaluation of O-[11C]methyl-L-tyrosine for tumor imaging by positron emission tomography
Kiichi Ishiwata, Hideo Tsukada, Kazuo Kubota, Tadashi Nariai, Norihiro Harada, Kazunori Kawamura, Yuichi Kimura, Keiichi Oda, Ren Iwata, Kenji Ishii Nucl Med Biol. 2005 Apr;32(3):253-62. doi: 10.1016/j.nucmedbio.2004.11.005.
We performed preclinical and clinical studies of O-[11C]methyl-L-tyrosine, a potential tracer for imaging amino acid transport of tumors by positron emission tomography (PET). Examinations of the radiation-absorbed dose by O-[11C]methyl-L-tyrosine and the acute toxicity and mutagenicity of O-methyl-L-tyrosine showed suitability of the tracer for clinical use. The whole-body imaging of monkeys and healthy humans by PET showed low uptake of O-[11C]methyl-L-tyrosine in all normal organs except for the urinary track and bladder, suggesting that the O-[11C]methyl-L-tyrosine PET has the potential for tumor imaging in the whole-body. Finally, the brain tumor imaging was preliminarily demonstrated.
3. Methylated derivatives of l-tyrosine in reaction catalyzed by l-amino acid oxidase: isotope and inhibitory effects
Małgorzata Pająk J Biochem. 2020 Nov 1;168(5):509-514. doi: 10.1093/jb/mvaa066.
l-Amino acid oxidase (LAAO) is widely distributed in nature and shows important biological activity. It induces cell apoptosis and has antibacterial properties. This study was designed to investigate the effect of methyl substituent on its activity as methylated derivatives of l-tyrosine, labelled with short-lived B+ emitters, have been used in oncological diagnostics. To study isotope effects in the oxidative deamination of O-methyl-l-tyrosine, the deuterated isotopomer, i.e. O-methyl-[2-2H]-l-tyrosine, was synthesized by isotope exchange, catalyzed enzymatically by tryptophanase. Isotope effects were determined using the spectrophotometric non-competitive method. The values of isotope effects indicate that the α-C-H bond cleavage occurs in the rate determining step of the investigated reaction and α-hydrogen plays a role in the substrate binding process at the enzyme active site. The inhibitory effect on LAAO activity was studied with α-methyl-l-tyrosine and N-methyl-l-tyrosine. The mode of inhibition was determined based on Lineweavear-Burk plots intersections. α-Methyl-l-tyrosine has been found a mixed type inhibitor of the investigated enzyme, whereas N-methyl-l-tyrosine is a non-competitive inhibitor of LAAO.
