Modification of maize phosphoenolpyruvate carboxylase by Woodward's reagentK

Maize leaf phosphoenolpyruvate carboxylase was completely and irreversibly inactivated by treatment with micromolar concentrations of Woodward's reagentK (WRK) for about 1 min. The inactivation followed pseudo-first-order reaction kinetics. The order of reaction with respect to WRK showed that the reagent causes formation of reversible enzyme inhibitor complex before resulting in irreversible inactivation. The loss of activity was correlated to the modification of a single carboxyl group per subunit, even though the reagent reacted with 2 carboxyl groups per protomer. Substrate PEP and PEP + Mg²⁺ offered substantial protection against inactivation by WRK. The modified enzyme showed a characteristic absorbance at 346 nm due to carboxyl group modification. The modified enzyme exhibited altered surface charge as seen from the elution profile on FPLC Mono Q anion exchange column. The modified enzyme was desensitized to positive and negative effectors like glucose-6-phosphate and malate. Pretreatment of PEP carboxylase with diethylpyrocarbonate prevented WRK incorporation into the enzyme, suggesting that both histidine and carboxyl groups may be closely physically related. The carboxyl groups might be involved in metal binding during catalysis by the enzyme.     

Thromboxane receptor antagonism combined with thromboxane synthase inhibition. 7. pyridinylalkyl-substituted arylsulfonylamino arylalkanoic acids.

Arylsulfonylamino arylalkanoic acids substituted with a pyridinylalkyl group on the arylalkanoic acid portion of the molecule were synthesized and found to behave as thromboxane receptor antagonists (TxRAs) and thromboxane synthase inhibitors (TxSIs). One of these compounds (11), with a 1,3,5-trisubstituted central aromatic ring was demonstrated to have good functional bioavailability and efficacy as a platelet inhibitor in guinea pigs.     

Activation and inhibition of spinach ribulose 1,5-bisphosphate carboxylase by 2-phosphoglycolate

Ribulose 1,5-bisphosphate carboxylase when activated by preincubation with 1 mM bicarbonate and 10 mM magnesium chloride can be further activated ca 20–500% by incubating with 2.5 mM phosphoglycolate depending upon the pH of the preincubation medium. The activation effects were seen only under specific preincubation conditions. The activation by phosphoglycolate was a slow reaction requiring ca 15 min for maximal effect. Even though magnesium was essential for phosphoglycolate activation, concentrations higher than 15 mM progressively inhibited the activation of the enzyme by phosphoglycolate. When added directly to the reaction mixture, phosphoglycolate was a potent inhibitor of the carboxylase activity. Even under preincubating conditions, phosphoglycolate showed slight inhibitory effect at 0.1 mM and activation was observed at concentrations higher than 0.5 mM. The K_A value for phosphoglycolate was 2.8 mM.     

Evidence for the involvement of superoxide anions in the oxygenase reaction of ribulose-1,5-diphosphate carboxylase.

The mechanism of oxygenase reaction catalysed by ribulose-1,5-diphosphate carboxylase was investigated using superoxide dismutase from bovine erythrocytes. Inclusion of superoxide dismutase in the assay mixture resulted in strong inhibition of oxygenase reaction. Ribulose-1,5-diphosphate was found to compete for superoxide anions with dismutase and nitroblue tetrazolium which also inhibited the oxygenase reaction. These observations indicate the possible involvement of superoxide anions in the oxygenase reaction.     

SUMO fosters assembly and functionality of the MutSγ complex to facilitate meiotic crossing over

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Uses of the rectus femoris myocutaneous flap.

The rectus femoris myocutaneous flap is quite useful for definitive immediate coverage of complex wounds within its territorial arc. We describe 4 cases to illustrate the capabilities of this flap. The indications for, the anatomy of, and the surgical technique for transfer, as well as the functional sequelae in two nonparaplegic patients are discussed.