PubMed Health⌕ Search

Biomedical subjects

C L Borders

Publications and source records attributed to C L Borders.

9 recordsLinked to original sources
PubMed1979

Chemical modification of histidyl and lysyl residues in yeast enolase.

Modification of yeast enolase (2-phospho-D-glycerate hydro-lyase, EC 4.2.1.11) by diethyl pyrocarbonate at either pH 6.1 or 6.6 caused a biphasic inactivation of the enzyme. In the presence of excess Mg2+, either an equilibrium mixture of substrates or 3-phosphoglycerate, a competitive inhibitor, prevented the second slower phase of inactivation, but had no effect on the first rapid phase. Complete inactivation by diethyl pyrocarbonate correlates with the modification of six histidyl residues/subunit, while 3-phosphoglycerate protects two histidyl residues/subunit from modification. Modification of enolase by two lysine-specific reagents, 2,4,6-trinitrobenzenesulfonate and pyridoxal 5'-phosphate, at pH 8.3 caused a slow loss of enzyme activity. However, substrates did not significantly protect against inactivation by either reagent, and inactivation with 2,4,6-trinitrobenzenesulfonate correlates with the modification of 18 lysyl residues/enzyme subunit.

Binding Sites↗
PubMed1978

Role of arginyl residues in yeast hexokinase PII.

Yeast hexokinase PII is rapidly inactivated (assayed at pH 8.0) by either butanedione in borate buffer or phenylglyoxal, reagents which are highly selective for the modification of arginyl residues. MgATP alone offers no protection against inactivation, consistent with low affinity of hexokinase for this nucleotide in the absence of sugar. Glucose provides slight protection against inactivation, while the combined presence of glucose and MgATP gives significant protection, suggesting that modified arginyl residues may lie at the active site, possibly serving to bind the anionic polyphosphate of the nucleotide in the ternary enzyme:sugar:nucleotide complex. Extrapolation to complete inactivation suggests that inactivation by butanedione correlates with the modification of 4.2 arginyl residues per subunit, and complete protection against inactivation by the combined presence of glucose and MgATP correlates with the protection of 2 to 3 arginyl residues per subunit. When the modified enzyme is assayed at pH 6.5, significant activity remains. However, modification by butanedione in borate buffer abolishes the burst-type slow transient process, observed when the enzyme is assayed at pH 6.5, to such an extent that after extensive modification the kinetic assays are characterized by a lag-type slow transient process. But even after extensive modification, hexokinase PII still demonstrates negative cooperativity with MgATP and is still strongly activated by citrate when assayed at pH 6.5.

Arginine↗
PubMed1977

Arginyl residues: anion recognition sites in enzymes.

Chemical modification with 2,3-butanedione in borate buffer indicates that nine of ten glycolytic enzymes studied contain arginyl residues at their active sites. Fructose-1,6-diphosphatase also has arginines at its binding site for the allosteric inhibitor, adenosine monophosphate. These and other data suggest that, as a general rule, enzymes acting on anionic substrates or cofactors will probably contain arginyl residues as components of their ligand binding sites. This could account in part for the relatively infrequent occurrence of arginine in proteins.

Adenosine Monophosphate↗
PubMed1975

An essential arginyl residue at the nucleotide binding site of creatine kinase.

Treatment of rabbit muscle creatine kinase (EC 2.4.3.2) with either butanedione in borate buffer or phenylglyoxal in Veronal buffer decreases enzymatic activity correlating with the modification of a single arginyl residue per subunit of the dimeric enzyme. Very little activity is lost when modification is performed in the presence of MgATP or MgADP. Nucleotide binding to the modified enzyme is virtually abolished as determined by ultraviolet difference spectroscopy. The data suggest that an arginyl residue plays an essential role in the enzymatic mechanism of creatine kinase, probably as a recognition site for the negatively charged oligophosphate moiety of the nucleotide.

Adenine Nucleotides↗