11. This reaction, called tRNA charging, is catalyzed by aminoacyl tRNA synthetase . 12. Mutations in the " HLCS " gene cause holocarboxylase synthetase deficiency. 13. Argininosuccinate synthetase is a homotetramer, with each subunit consisting of 412 residues. 14. Holocarboxylase synthetase may also play a role in regulating the activity of genes. 15. No one has examined experimentally the arginine-tRNA synthetase of these organisms. 16. Mutations in the " GSS " gene cause glutathione synthetase deficiency. 17. Glutathione synthetase is important for a variety of biological functions in multiple organisms. 18. This enzyme is also called "'phosphopantothenoylcysteine synthetase " '. 19. Aspartyl-tRNA synthetase charges its cognate tRNA with aspartate during protein biosynthesis. 20. This gene encodes the mitochondrial tryptophanyl-tRNA synthetase .