Isolation and some properties of glycated D-glyceraldehyde-3-phosphate dehydrogenase from rabbit muscle.
Glycated D-glyceraldehyde-3-phosphate dehydrogenases (GAPDH) from rabbit muscle and human erythrocytes have been investigated. The specific activity of the non-glycated GAPDH from rabbit muscle is approx. 180 units. (One unit is defined as the specific activity required to convert 1 microM of substrate/min per mg of enzyme.) The activity of the glycated enzyme, consisting of two sugars per tetramer, is lower than that of the non-glycated GAPDH. Non-enzymic transamination of the N-termini of glycated GAPDH (gGAPDH) indicates that they are not blocked by glycation. The rate of modification of thiols (Cys-149) with 5,5'-dithiobis-(2-nitrobenzoic acid) was greater for the glycated than the non-glycated enzymes. The rate of modification of amino groups of Lys residues of gGAPDH with o-phthalaldehyde was greater for the non-glycated enzyme. In 0.18 M guanidine-HC1 solution, the emission intensity at 410 nm of a fluorescent NAD+ derivative introduced into the active site decreased to 80%, whereas that of gGAPDH decreased to 50%. This suggests that the glycated sites are near the active site; glycation of the enzyme leads to a change of the microenvironment of Cys-149, alters the conformation of the active site and decreases the activity.
He
R Q
RQ
National Laboratory of Biomacromolecules, Academia Sinica, Beijing, People's Republic of China.
Yang
M D
MD
Zheng
X
X
Zhou
J X
JX
D000818:Animals; D001665:Binding Sites; D002846:Chromatography, Affinity; D002852:Chromatography, Ion Exchange; D004912:Erythrocytes / Q000201:enzymology; D005947:Glucose / Q000378:metabolism; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D006801:Humans; D009132:Muscles / Q000201:enzymology*; D011487:Protein Conformation; D011817:Rabbits
D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D005947:Glucose