Pyridoxal phosphate, amino mutase

Lysine mutase is the first of a group of AdoCbl-dependent enzymes that catalyses the 1,2-migration of an amino group (Fig. 26). It has been isolated from Clostridium sticklandii [39] and consists of a cobalamin-binding orange protein and a smaller yellow protein. Apart from AdoCbl, several other essential cofactors have been identified, such as pyridoxal phosphate, ATP, FAD, thiols, Mg2+ and K+ [38]. The function of the yellow protein and some of these cofactors is to renew continuously... 

The amino mutases require pyridoxal phosphate for activity, and although little is known about them mechanistically, Freyis work on lysine 2,3-aminomutase has proved very informative (Lieder et al., 1998 Frey, 1997). Lysine 2,3-aminomutase is not a 1 2 enzyme but it functions very similarly (Section 1). The enzyme uses pyridoxal phosphate to facilitate the 1,2... 

Aminomutases. The enzymes L-p-lysine mutase (which is also D-a-lysine mutase) and D-omithine mutase catalyze the transfer of an co-amino group to an adjacent carbon atom (Table 16-1). Two proteins are needed for the reaction pyridoxal phosphate is required and is apparently directly involved in the amino group migration. In the P-lysine mutase the 6-amino group of L-P-lysine replaces the pro-S hydrogen at C-5 but with inversion at C-5 to yield (3S, 5S)-... 

In biochemical parlance, these systems are called mutases, or sometimes isomerases. When Z = OH and Y = OH or NHj, the product eliminates an aldehyde and either HjO or NH3 so that the process is irreversible. Such systems sometimes are referred to as eliminases, dehydrases or ammonia-lyases. Examples of these various types of systems are shown by the first five examples in Figure 8.3, where (CoA)—S represents coenzyme A. It should be noted that the amino mutases, such as ornithine amino mutase, also require pyridoxal phosphate as a cofactor. 

To emphasize some of the common features, these systems have been separated into three classes Class I are the mutases, such as glutamate mutase, in which a C—C bond is broken, and all exist in the base-off/hist-on form Class II are the eliminases which involve C—O or C—N bond cleavage and ribonuleotide triphosphate reductase, and are in the base-on form Class III are the amino mutases which interchange H and NH2 and require pyridoxal phosphate as a cofactor. The structure of one member of this class has b n determined and found to be in the base-off/hist-on form. The pyridoxal phosphate is covalently bonded to a lysine, Lys-NHj, of the peptide, as shown in the following reaction ... 

---