The Amino Acid Composition and Other Properties of Thermostable Glyceraldehyde 3-Phosphate Dehydrogenase from Bacillus stearothermophilus

The molecular weight of the thermophilic glyceraldehyde 3-phosphate dehydrogenase was evaluated by the sedimentation equilibrium method and found to be 163,500 ± 4,000. The s20, w0 is 7.17 × 10−13 sec; the D20, w0 is 3.95 × 10−7 cm2 sec−1. Using electrophoresis on cellulose acetate strips, the isoelectric pH was found to be approximately 4.6. The amino acid composition of the enzyme is quite similar to counterparts from other sources; there are 1,384 amino acid residues per molecule. The enzyme contains 4 eq of bound NAD+ and four sulfhydryl groups and these findings in conjunction with the amino acid content are indicative of a tetrameric structure. Levels of hydrophobicity were calculated for the thermophilic glyceraldehyde 3-phosphate dehydrogenase and compared with proteins from other sources. The average hydrophobicity of the thermophilic glyceraldehyde 3-phosphate dehydrogenase was found to be close to that of other glyceraldehyde 3-phosphate dehydrogenases and it was concluded that this parameter need not be an indication of thermostability. The general similarities between the thermophilic glyceraldehyde 3-phosphate dehydrogenase described here and other glyceraldehyde 3-phosphate dehydrogenases make a mechanism of thermophily for this enzyme unclear. Further structural work is in progress to elucidate a mechanism.