Limited proteolysis by trypsin influences activity of maize phosphoenolpyruvate carboxylase.
Maize phosphoenolpyruvate carboxylase (PEPC) was rapidly and completely inactivated by very low concentrations of trypsin at 37 degrees C. PEP+Mg2+ and several other effectors of PEP carboxylase offered substantial protection against trypsin inactivation. Inactivation resulted from a fairly specific cleavage of 20 kDa peptide from the enzyme subunit. Limited proteolysis under catalytic condition (in presence of PEP, Mg2+ and HCO3) although yielded a truncated subunit of 90 kDa, did not affect the catalytic function appreciably but desensitized the enzyme to the effectors like glucose-6-phosphate glycine and malate. However, under non-catalytic condition, only malate sensitivity was appreciably affected. Significant protection of the enzyme activity against trypsin during catalytic phase could be either due to a conformational change induced on substrate binding. Several lines of evidence indicate that the inactivation caused by a cleavage at a highly conserved C-terminal end of the subunit.
Maralihalli
G
G
Molecular Biology and Agriculture Division, Bhabha Atomic Research Centre, Trombay, Mumbai.
Bhagwat
A S
AS
D001639:Bicarbonates / Q000494:pharmacology; D005453:Fluorescence; D019298:Glucose-6-Phosphate / Q000494:pharmacology; D005998:Glycine / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008293:Malates / Q000494:pharmacology; D010730:Phosphoenolpyruvate Carboxylase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D011487:Protein Conformation; D013438:Sulfhydryl Compounds / Q000737:chemistry; D014357:Trypsin / Q000494:pharmacology*; D003313:Zea mays / Q000201:enzymology*
D001639:Bicarbonates; D008293:Malates; D013438:Sulfhydryl Compounds; D019298:Glucose-6-Phosphate; D014357:Trypsin; D010730:Phosphoenolpyruvate Carboxylase; D008274:Magnesium; D005998:Glycine