Crystallization and preliminary X-ray diffraction data for a purple acid phosphatase from sweet potato

Purple acid phosphatase from sweet potato is a homodimer of 110 kDa. Two forms of the enzyme have been characterized. One contains an Fe±Zn centre similar to that previously reported for red kidney bean purple acid phosphatase. Another isoform, the subject of this work, is the ®rst con®rmed example of an Fe±Mn-containing enzyme. Crystals of this protein have been grown from PEG 6000. They have unit-cell parameters a = b = 118.4, c = 287.4 A Ê and have the symmetry of space group P6522, with one dimer per asymmetric unit. Diffraction data collected using a conventional X-ray source from a cryocooled crystal extend to 2.90 A Ê resolution. The three-dimensional structure of the enzyme will provide insight into the coordination of this novel binuclear metal centre

Rapid serum tube technology overcomes problems associated with use of anticoagulants

Introduction: Failure to obtain complete blood clotting in serum is a common laboratory problem. Our aim was to determine whether snake prothrombin activators are effective in clotting blood and producing quality serum for analyte measurement in anticoagulated patients. Materials and methods: Whole blood clotting was studied in a total of 64 blood samples (41 controls, 20 Warfarin patients, 3 anticoagulated patients using snake venom prothrombin activator (OsPA)) with plain tubes. Coagulation was analysed using a visual assay, Hyland-Clotek and thromboelastography. Healthy control blood was spiked with a range of anticoagulants to determine the effectiveness of OsPa-induced clotting. A paired analysis of a Dabigatran patient and a control investigated the effectiveness of the OsPA clotting tubes. Biochemical analytes (N = 31) were determined for 7 samples on chemistry and immunoassay analysers and compared with commercial tubes. Results: Snake venom prothrombin activators efficiently coagulated blood and plasma spiked with heparin and commonly used anticoagulants. Clotting was observed in the presence of anticoagulants whereas no clotting was observed in BDRST tubes containing 3 U/mL of heparin. Snake venom prothrombin activator enhanced heparinised blood clotting by shortening substantially the clotting time and improving significantly the strength of the clot. Comparison of 31 analytes from the blood of five healthy and two anticoagulated participants gave very good agreement between the analyte concentrations determined. Conclusions: Our results showed that the snake venom prothrombin activators OsPA and PtPA efficiently coagulated recalcified and fresh bloods with or without added anticoagulants. These procoagulants produced high quality serum for accurate analyte measurement

A purple acid phosphatase from sweet potato contains an antiferromagnetically coupled binuclear Fe-Mn center

A purple acid phosphatase from sweet potato is the first reported example of a protein containing an enzymatically active binuclear Fe-Mn center. Multifield saturation magnetization data over a temperature range of 2 to 200 K indicates that this center is strongly antiferromagnetically coupled. Metal ion analysis shows an excess of iron over manganese. Low temperature EPR spectra reveal only resonances characteristic of high spin Fe(III) centers (Fe(III)-apo and Fe(III)-Zn(II)) and adventitious Cu(II) centers. There were no resonances from either Mn(II) or binuclear Fe-Mn centers. Together with a comparison of spectral properties and sequence homologies between known purple acid phosphatases, the enzymatic and spectroscopic data strongly indicate the presence of catalytic Fe(III)-Mn(II) centers in the active site of the sweet potato enzyme. Because of the strong antiferromagnetism it is likely that the metal ions in the sweet potato enzyme are linked via a mu -oxo bridge, in contrast to other known purple acid phosphatases in which a mu -hydroxo bridge is present. Differences in metal ion composition and bridging may affect substrate specificities leading to the biological function of different purple acid phosphatases

On the mechanism of the reaction of tris(hydroxymethyl)aminomethane with activated carbonyl compounds: A model for the serine proteinases

The pH dependence of the reaction of tris(hydroxymethyl)aminomethane (Tris) with the activated carbonyl compound 4-trans-benzylidene-2-phenyloxazolin-5-one (I) is given by the equation k′ = kK (K + [H]) + k[OH]K (K + [H]), where K is the dissociation constant of TrisH. Spectrophotometric experiments show that the Tris ester of α-benzamido-trans-cinnamic acid is formed quantitatively over a range of pH values, regardless of the relative contribution of k and k terms to k′. Hence, both terms refer to alcoholysis. While the mechanism of the reaction is not determined unequivocally in the present work, the magnitude of the k term, together with its dependence on the basic form of Tris, suggests that ester formation is occurring by nucleophilic attack of a Tris hydroxyl group on the carbonyl carbon of the oxazolinone, with intramolecular catalysis by the Tris amino group. The rate enhancement due to this group is at least 10 and possibly of the order 10. This system is compared with other model systems for the acylation step of catalysis by serine esterases and proteinases

Evaluation of Equilibrium Constants for the Binding of N-Acetyl-L-tryptophan to Monomeric and Dimeric Forms of α-Chymotrypsin

The binding of N-acetyl-l-tryptophan to the monomeric and dimeric forms of α-chymotrypsin in I=0.2 acetate-chloride buffer, pH 3.86, has been studied quantitatively. Equilibrium sedimentation studies in the absence of inhibitor yielded a dimerization constant of 3.5 L/g. This value was confirmed by frontal gel chromatography of the enzyme on Bio-Gel P-30, which was also used to establish that N-acetyl-L-tryptophan binds preferentially to monomeric enzyme. From kinetic studies of competitive inhibition with N-acetyl-l-tryp-tophan ethyl ester as substrate, an equilibrium constant of 1300 M-1 was determined for the binding of N-acetyl-l-tryptophan to monomeric α-chymotrypsin. An intrinsic binding constant of 250 M-1 for the corresponding interaction with dimeric enzyme was calculated on the basis of these results and binding data obtained with concentrated (18.5 g/L) a-chymotrypsin. The present results refute earlier claims for exclusive binding of competitive inhibitors to monomer and also those for equivalence of inhibitor binding to monomeric and dimeric forms of a-chymotrypsin