Reaction heat variation with pH in formation of the trypsin-soybean inhibitor complex.

The heat of reaction between beta-trypsin and Kunitz soybean inhibitor (STI) hasbeen measured at 5 degrees and 25 degrees from pH 4 to 8.5. Corresponding measuremenportion of tRNA-Gly2-GGA/G molecules isolated from E. coli cells. The missense suppressor mutation, glyTsuA36(HA), results in a C yields U base substitution at the 3' end of the anticodon of tRNA-Gly2-GGA/G(nucleotide position 38). Asecondary effect of this base substitution is the modification of the A residue directly adjacent to the 3' end of the anticodon of tRNA-Gly2-suA36(HA), suggesting that the enzymes responsible for this modification recognize the anticodon sequencesof prospective tRNA substrates. The creation of a missense-suppressing tRNA, tRNA-Gly2-suA36(HA), by an alteration of the anticodon sequence of tRNA-Gly2-GGA/G is analogous to mechanisms whereby other suppressor tRNAs have arisen. The high degree of nucleotide sequence homology between the amino acid acceptor stems and anticodon regions may be recognized by the glycyl-tRNA synthetase; the involvement of theanticodon region in the synthetase recognition process is supported by the greatly decreased rate of aminoacylation of tRNA-Gly2-suA36(HA).