Vitamin B6-polypeptide systems

In a similar approach, pyridoxamine was introduced into an S-peptide at position 8 to maintain the interactions with His12 and HisU9 [30]. Upon formation of the RNase complex, the rate was enhanced 7-fold compared with uncomplexed peptides under single turnover conditions. However, replacing the His residue at position 12 with Ser afforded only a 3-fold rate increase for the S-peptide-S-protein complex. Under catalytic conditions with pyruvate and L-phenylalanine as the substrates, uncomplexed peptides did not show catalytic turnover, suggesting that a hydrophobic microenvironment in the peptide-protein complex is critical for catalysis. However, in the presence of the S-protein, catalysis ensued. Up to 1.5 turnovers were observed in 160 h from the S-peptide-S-protein complex. 

Further studies on these protein-pyridoxamine conjugates were devoted to the turnover behaviors, metal ion effects, and effects of pyridine quaternization [34], As many 

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Vitamin B6 enzyme models that can catalyze five types of reactions - transamination, racemization, decarboxylation, P-elimination and replacement, and aldolase-type reactions - have been reviewed. There are also five approaches to construct the vitamin B6 enzyme models (i) vitamin B6 augmented with basic or chiral auxiliary functional groups (ii) vitamin B6 having an artificial binding site (iii) vitamin B6-surfactant systems (iv) vitamin B6-polypeptide systems (v) polymeric and dendrimeric vitamin B6 systems. These model systems show rate enhancement and some selectivity in vitamin B6-dependent reactions, but they are still primitive compared with the real enzymes. We expect to see improved reaction rates and selectivities in future generations of vitamin B6 enzyme models. An additional goal, which has not received ade-... 

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