Photoinactivation of Aldolases by Pyridoxal Phosphate and Its Analogues

AUTOR(ES)

Davis, L. C.

RESUMO

Pyridoxal phosphate can act as a specific photosensitizer for amino acid residues in rabbit muscle and spinach leaf aldolases, but the residues affected depend on the pH of the reaction. Below pH 8 one histidine residue per enzyme subunit is destroyed; above pH 8.5 there is little loss of histidine, and photoinactivation is associated with the destruction of specific tyrosine residues, particularly the COOH-terminal residues. Pyridoxal and 4-pyridinecarboxaldehyde are much less effective than pyridoxal phosphate at neutral pH, but are similar to pyridoxal phosphate in their photosensitizing activity at the higher pH. Compounds lacking the aldehyde group or the pyridine ring show little or no activity. A number of other enzymes, including α-glycerophosphate dehydrogenase, glucose-6-phosphate dehydrogenase, and yeast hexokinase, were also photoinactivated in the presence of pyridoxal phosphate; however, rabbit liver aldolase and two isomerases tested were completely resistant. The results suggest that certain enzymes, including rabbit muscle and spinach aldolases, but not rabbit liver aldolase, contain a specific site which interacts with pyridoxal phosphate, and that the conformation of this site changes in the pH range between 8.0 and 8.5

Documentos Relacionados

• Coenzymatic Activity of Pyridoxal 5′-Sulfate and Related Analogues of Pyridoxal 5′-Phosphate
• A fluorimetric method for the measurement of pyridoxal and pyridoxal phosphate in human plasma and leucocytes, and its application to patients with sideroblastic marrows.
• PYRIDOXAL KINASE OF HUMAN BRAIN AND ITS INHIBITION BY HYDRAZINE DERIVATIVES*
• Coenzymatic activity of homologues of pyridoxal phosphate.
• Action Spectra of Photomorphogenic Induction and Its Photoinactivation. 123