PLP is seen bound covalently to the active sites of aminotransferases via structure determination The reaction occurs via a typical ping-pong mechanism: the first product leaves before the second substrate enters An interconversion between an aldimine(醛亚胺 and a ketimine(酮亚胺) is proposed to occur via a quinonoid(醌烈的) intermediate during the transamination reaction. PLP act in a variety of other reactions at the a, B and y carbons of amino acids, including racemization, decarboxylations at the a carbon, elimination and replacement reactions at the B andy carbons
• PLP is seen bound covalently to the active sites of aminotransferases via structure determination. • The reaction occurs via a typical ping-pong mechanism: the first product leaves before the second substrate enters. • An interconversion between an aldimine（醛亚胺） and a ketimine（酮亚胺） is proposed to occur via a quinonoid（醌型的） intermediate during the transamination reaction. • PLP act in a variety of other reactions at the a, b, and g carbons of amino acids, including racemizations, decarboxylations at the a carbon, elimination and replacement reactions at the b and g carbons
cOo COO C=O COO H3N-C-H COO PLP CH2 +HRN-C--H CHo+ C-0 aminotransferase CH 2 R CH 2 R COO COo a-Ketoglutarate L-Amino acid L-Glutamate a-Keto acid Aspartic ai inietraynsferase (dimeric) PLP (c)
Aspartate aminotransferase (dimeric) PLP
O-P=0 CH2 H NH OH CH3 Pyridoxal phosphate (PLP) O-P=0 O CH2 H H3N-一 NH H oH CH Pyridoxamine p hosphate
O-P CHe H EnzLys-NH2 O-C OH CH H2O O-—P=0 ) CH HH 2-methyl-ASp-PLP Enz-Lys-N NH Schiff base OH CH3 b PLP accepts and donates amino groups in the active (e) I site of aminotransferases
2-methyl-Asp-PLP PLP accepts and donates amino groups in the active site of aminotransferases
H-C-CO0 R--C-cOO "NH, L-Amino H-C-COO C=C00 R-C-coo coo " NH HO CH HO HO HO C Schiff base Carbanion Quinonoid intermediate Ketimine Pyridoxal phosphate intermediate Pyridoxamine (aldimine form phospha on PLP facilitates En transamination, racemization, Q R-NHCOO H," -SHL, D-amino decarboxylation Pyridoxal of amino acids Limine) R H-C H-C-H NH HO NH, Amine CH- HO Pyridoxal phosphat Carbamic Quinonoid intermediate
Ketimine PLP facilitates transamination, racemization, decarboxylation of amino acids