Affinity labeling of the inhibitory DPNH site of bovine liver glutamate dehydrogenase by 5'-fluorosulfonylbenzoyl adenosine.

A new adenosine analogue has been synthesized, 5'-fluorosulfonylbenzoyl adenosine, which reacts covalently with bovine liver glutamate dehydrogenase with the incorporation of approximately 1 mol of 5'-sulfonylbenzoyl adenosine per peptide chain. Native glutamate dehydrogenase is known to be inhibited by relatively high concentrations of DPNH by binding to a second noncatalytic site; the major change in the kinetic characteristics of the modified enzyme is a total loss of this inhibition by DPNH. The modified enzyme retains full catalytic activity as measured in the absence of allosteric ligands, is still inhibited more than 90% by GTP, and is activated normally by ADP. These results demonstrate that the catalytic as well as the GTP and ADP regulatory sites are distinct from the inhibitory DPNH site. The rate constant for reaction of 5'-fluorosulfonylbenzoyl adenosine is decreased by high concentrations of DPNH alone or by DPNH plus GTP, but not by the substrate alpha-ketoglutarate, the coenzymes DPN or TPNH, or the regulators ADP or GTP alone. These observations are consistent with the postulate that the 5'-fluorosulfonylbenzoyl adenosine attacks exclusively the second inhibitory DPNH site. The DPNH inhibition is abolished when an average of only 0.5 mol of 5'-sulfonylbenzoyl adenosine per peptide chain has been incorporated. The structure of 5'-fluorosulfonylbenzoyl adenosine is critical in determining the course of the modification reaction. The smaller compound p-fluorosulfonylbenzoic acid does not affect the kinetic characteristics of the enzyme, and the isomeric compound 3'-fluorosulfonylbenzoyl adenosine produces a different pattern of changes in the regulatory properties (Pal. P. K., Wechter, W. J., and Colman, R. F. (1975) Biochemistry 14, 707-715). Indeed, enzyme which has combined stoichiometrically with 5'-fluorosulfonylbenzoyl adenosine is still able to react with 3'-fluorosulfonylbenzoyl adenosine; thus, the two adenosine analogues appear to react at distinct sites on glutamate dehydrogenase. It is proposed that 5'-fluorosulfonylbenzoyl adenosine will be complementary to 3'-fluorosulfonylbenzoyl adenosine as a general affinity label for dehydrogenases as well as other classes of enzymes which use adenine nucleotides as substrates or regulators.     

Comparative studies on the structural phosphoproteins of mammalian type C viruses.

The major phosphoprotein common to woolly monkey sarcoma virus, gibbon ape lymphosarcoma virus, and type C viruses of the lower mammalian species (mouse, rat, cat), with the exception of the endogenous cat virus (RD-114), is the polypeptide of about 12,000 molecular weight. The protein-phosphate bond in this polypeptide of several viruses is of the phosphoserine variety excepting gibbon ape virus, which contains both phosphoserine and phosphothreonine. The primary phosphoprotein of RD-114 virus and the endogenous baboon type C virus, on the other hand, is the polypeptide of about 15,000 molecular weight which contains phosphothreonine as its phosphoamino acid. A second major phosphoprotein of molecular weight of 10,000 is detected only in viruses genetically related to rat species including those derived from the RPL cell line, from Sprague-Dawley rat embryo cells, and the Kirsten mouse sarcoma virus which was recovered from a mouse erythroblastosis virus after in vivo propagation through rat. These phosphorylated polypeptides of molecular weight 15,000, 12,000, or 10,000 are present in the virion structure in several different but nonrandom phosphorylated states.     

Phosphoproteins: structural components of oncornaviruses.

Oncornaviruses, which contain a virion-associated protein kinase, were found to possess phosphoproteins as virion structural components. One major phosphoprotein common to strains of laboratory and wild mouse oncornaviruses and a strain of feline leukemia virus was shown to be a polypeptide of about 12, 000 mol wt. In addition to this, the Kirsten strain of murine sarcoma virus contained a second major phosphoprotein of about 10, 000 mol wt, and mouse erythroblastosis virus contained a second major phosphoprotein that was either identical to or comigrated with the virion glycoprotein of about 74, 000 mol wt. The major phosphoprotein of RD-114 virus was found to be of about 16, 000 mol wt. The major phosphoamino acid of the 12, 000-mol wt polypeptide of the mouse erythroblastosis virus was identified as phosphoserine, and that of the 16, 000-mol wt polypeptide of the RD-114 virus was identified as phosphothreonine.     

Purification and properties of cis-aconitic decarboxylase

Summary Lyophilized and stored in a deep-freeze, the mycelial material was found to retain cis-aconitic decarboxylase activity unimpaired at the end of 2 months. Mycelia could be stored also in the frozen condition but after squeezing hard to remove as much of adherent water as possible. Extracts with maximum cis-aconitic decarboxylase activity were obtained when the frozen or better the lyophilized mycelia of Aspergillus terreus were ground in a mortar with phosphate buffer using pyrex glass powder as abrasive. Cis-aconitic decarboxylase was purified 25-fold by fractionation with ammonium sulfate, starting from extracts of the mycelia in phosphate buffer. The purified enzyme was considerably more stable than the crude extracts to storage and dialysis. The optimum pH was 5.8 using 0.2 m phosphate buffer; Km value was 5×10^-3 m at pH 5.8 and 37°C. EDTA and 8-hydroxyquinoline activated the enzyme; all metals tested inhibited the enzyme, Zn⁺⁺ and Cu⁺⁺ leading to complete inactivation. Fluoride, arsenite and azide also inhibited the enzyme activity.     

MsrA Efflux Pump Inhibitory Activity of Piper cubeba L.f. and its Phytoconstituents against Staphylococcus aureus RN4220

MsrA, an efflux pump belonging to ATP‐binding cassette (ABC) transporter family that conferred resistance to macrolides, was detected in Staphylococcus aureus strains. Herein, we report the isolation of phytoconstituents from Piper cubeba fruit methanol extract and investigated their efflux pump inhibitory potential against S. aureus MsrA pump. Four isolated compounds, viz. pellitorine, sesamin, piperic acid and tetrahydropiperine studied in combination with erythromycin in S. aureus RN4220, exhibited 2–8‐fold reduction in minimum inhibitory concentration (MIC) of erythromycin. Pellitorine and sesamin decreased MIC of erythromycin by 8‐fold. The real‐time fluorometry‐based efflux and accumulation studies of ethidium bromide (EtBr) on S. aureus RN4220 in the presence of these compounds showed reduced efflux and enhanced uptake, thus indicating inhibition of the efflux pump. Pellitorine showed significant post‐antibiotic effect of erythromycin. The results revealed that the primary mechanism of action of these compounds involves steady ATP production impairment.