Large neutral amino acids composition

According to the lock-and-key model, an enzyme is pictured as a large, irregularly shaped molecule with a cleft, or crevice, in its middle. Inside the crevice is an active site, a small region with the shape and chemical composition necessary to bind the substrate and catalyze the appropriate reaction. In other words, the active site acts like a lock into which only a specific key can fit (Figure 24.10). An enzyme s active site is lined by various acidic, basic, and neutral amino acid side chains, all properly positioned for maximum interaction with the substrate. 

Petite mutants spontaneous mutants, chiefly yeasts, with chemical or physical defects in the respiratory chain. P. m. grow very slowly and form small ( petite ) colonies on nutrient agar. The same phenotype can be produced by a chromosomal mutation (segregational petite), or a mutation in the mitochondrial DNA (vegetative or neutral petite). In the latter case, mitochondrial structure is considerably altered, largely due to changes in the amino acid composition of the structural proteins of the inner mitochondrial membrane. Since these structural proteins are important for the correct arrangement and conformation of the respiratory chain enzymes, the effect of petite mutation on the respiratory chain is probably secondary. 

Amino acid compositions of the CGTases from 3 kinds 6f Bacillus were examined (9). None of the three enzymes contained cysteine, and the amounts of neutral and basic amino acids were similar. A relatively large amount of acidic amino acids was contained in the CGTase from B. ohbensis, which may be related to the acidity of the enzyme. 

---