Pyridoxal phosphate is a key cofactor in metabolism. Which one of the following best represents reactions that require this cofactor?
Pyridoxal phosphate, an aldehyde, interacts with an amino acid to form a Schiff base. Various products can be generated, depending on the enzyme (see Figure below).a. Amino acids are transaminated, decarboxylated, or deaminated in pyridoxal phosphate-requiring reactions.b. Pyridoxal phosphate is derived from vitamin B6 (pyridoxine).Pyridoxal phosphate is required for the activity of glycogen phosphorylase (the phosphorolysis of glycogen to glucose-1-phosphate), transaminases (such as transferring the nitrogen from aspartate to pyruvate to produce oxaloacetate and alanine), 3-elimination and addition reactions (exemplified by the condensation of serine and homocysteine to form cystathionine), and amino acid decarboxylations (histidine to histamine). Pyridoxal phosphate is not required for the conversion of homocysteine to methionine because that reaction requires N5-methyltetrahydrofolate and vitamin B12 .The structures of pyridoxal phosphate
Glycogenn Converted to Glucose-1-Phosphate and Glycogenn-1 - yes; Pyruvate Plus Aspartate Producing Alanine and Oxaloacetate - yes; Homocysteine Plus N5-Methyl-THF Produces Methionine and THF - no; Homocysteine Plus Serine Produces Cystathionine - yes; Histidine Produces Histamine - yes
Glycogenn Converted to Glucose-1-Phosphate and Glycogenn-1 - yes; Pyruvate Plus Aspartate Producing Alanine and Oxaloacetate - yes; Homocysteine Plus N5-Methyl-THF Produces Methionine and THF - yes; Homocysteine Plus Serine Produces Cystathionine - no; Histidine Produces Histamine - yes
Glycogenn Converted to Glucose-1-Phosphate and Glycogenn-1 - yes; Pyruvate Plus Aspartate Producing Alanine and Oxaloacetate - yes; Homocysteine Plus N5-Methyl-THF Produces Methionine and THF - no; Homocysteine Plus Serine Produces Cystathionine - yes; Histidine Produces Histamine - no
Glycogenn Converted to Glucose-1-Phosphate and Glycogenn-1 - yes; Pyruvate Plus Aspartate Producing Alanine and Oxaloacetate - no; Homocysteine Plus N5-Methyl-THF Produces Methionine and THF - yes; Homocysteine Plus Serine Produces Cystathionine - no; Histidine Produces Histamine - no
Proteins and Amino Acids