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The synthesis of a protein-reactive ATP analog, S-dinitrophenyl-6-mercaptopurine riboside 5'-triphosphate, started from isopropylidated 6-mercaptopurine. After dinitrophenylation, the thioester riboside was phosphorylated with POCI, and the monophosphate was converted to the triphosphate by activation with the aid of phosphoric acid diphenylester chloride, and reaction with inorganic pyrophosphate. and y-positions, was used for covalent binding of the nucleotide to rabbit muscle actin. In preparation for this affinity labelling, the one superficial --SH group of the protein had been alkylated with N-ethylmaleimide. The nucleotide was able to depolymerize N-ethylmaleimide-F-actin, and became attached to the G-form at a ratio of 0.8 molecules per actin monomer. The product could be repolymerized to the F-form with liberation of inorganic phosphate. The product could not be depolymerized after that by ATP solutions at low ionic strength.The analog, labelled with 32P in the A single radioactively labelled peptide was discerned in fingerprints of a tryptic digest.Actin, one of the two major filamentous proteins of the contractile system of muscle, possesses an unusual polymerization mechanism. The monomer form (G-actin) is isolated from acetone dry powder by extraction with ATP solutions of very low ionic content, each protomer binding one molecule of the nucleotide. Upon addition of magnesium or other salts, the bound triphosphate is hydrolyzed to ADP, and the ADP-protein complex polymerizes in a typical cooperative reaction (Engel, J., private communication) to double-helical filaments (Factin), present in muscle cells.The protein, except for slow and probably unphysiological recycling between F and G-forms, does not function as an ATPase. The binding and cleavage of the triphosphate however strongly resembles an enzymatic mechanism, coming to a stop after the one bound nucleotide has been hydrolyzed, before or during polymerization. Eur. J. Biochem. 43 (1974)binding site by X-(carboxynitrophenyl)-6-mercaptopurine riboside phosphate [I]. A related compound, X-dinitrophenyl-6-mercaptopurine riboside triphosphate, has now been obtained as an ATP analog, its synthesis and reaction with rabbit muscle actin are described. MATERIALS AND METHODSThe 6-mercaptopurine ribonucleoside, thioinosine was obtained from Waldhof Chemie (Mannheim). The protecting isopropylidene group was attached to the ribose moiety by the procedure of Hampton and Magrath [2]. Triethyl phosphate was distilled under vacuum not more than three weeks prior to use and kept over molecular sieve pearls (Merck (30.).Tetrasodium [32P]pyrophosphate (99.9 o/o asp, carrierfree) was obtained from the Amersham Radiochemical Centre (England). The solution was passed over a column of polysterene-sulfonic acid cation exchanger (Lewatit, Bayer) in the pyridinium form. The eluate was brought to dryness in a rotatory evaporator and traces of water were removed by adding 5ml dry pyridine, finally dry benzene, several times and evaporation of the solvent under vacuum. ...

A wide-band high-speed data acquisition system for electrical impedance tomography (EIT) is described. 32 active electrodes are used in the system, half of them as receive electrodes and the other half as drive electrodes. A buffer is mounted on the back of each receive electrode and a current source on each drive electrode. A multielectrode system with active electrodes was built to make it convenient to attach all the electrodes on the human thorax. The system is suitable for both dynamic imaging and multifrequency electrical impedance tomography (MFEIT). Its operating frequency can be chosen between 24 kHz and 400 kHz. Current is injected sequentially into 16 adjacent current electrode pairs and the 16 voltages between adjacent receive electrodes are measured for each current injection. ECG is collected to determine the relationship between the reconstructed images and cardiac activity. The collection of one frame of data is completed within 25 ms. The system has been successfully used for imaging the variation of conductivity distribution of the human thorax. The beat-by-beat cardiac-related change of conductivity distribution has been imaged by our system. The quasi-periodic variation of the impedance distribution can be seen from the image sequence with breath-holding.

The quantitative determination of biomass in a suspension by means of ultrasound velocity is a simple and on-line-applicable method. Such an ultrasonic sensor offers the advantage of being long-term stable, reliable, and sterilizable. In this paper we present sound velocity measurements made with different microorganisms. The experimental results which we have obtained with an impulse-echo method will be compared with theoretical predictions and discussed with respect to previous findings (Y. Ishimori, I.

The catalytic activity and activation energy of an enzyme are obtained by measuring the rate of the enzymic reaction at two different temperatures. With the aid of the Arrhenius equation, these two parameters can be used to calculate a value proportional to the quantity of enzyme. Using this approach to investigate the isoenzymes of creatine kinase, it was shown that the activation energy increased in the order creatine kinase MM, MB, BB. Mixtures of the isoenzymes showed an apparent mean activation energy, which likewise could be determined using the Arrhenius equation.Ageing of the isoenzymes results in an exponential decrease of catalytic activity, accompanied by a continuous increase in activation energy, the calculated quantity of enzyme remaining constant. Inactivation is therefore not an all-or-nothing process; rather a stepwise inactivation of individual molecules must be assutiied. The results of these ageing experiments and observations by other authors suggest that a similar inactivation occurs in vivo. Die kataly tische Aktivität und Aktivierungsenergie der Kreatinkinase-IsoenzymeZusammenfassung: Durch die Messung der Geschwindigkeit einer enzymatischen Reaktion bei zwei verschiedenen Temperaturen erhält man die kataly tische Aktivität und die Aktivierungsenergie des Enzyms. Aus beiden läßt sich gemäß der Arrhenius*Gleich\mg eine der Enzymmenge proportionale Größe berechnen. Mit dieser Methode untersuchten wir die Isoenzyme der Kreatinkinase und stellten fest, daß die Aktivierungsenergie in der Reihenfolge Kreatinkinase MM, MB und BB ansteigt. Mischungen der Isoenzyme zeigen eine scheinbare, mittlere Aktivierungsenergie, die sich ebenfalls mit der Arrhemus-Gleichung bestimmen läßt.Bei der Alterung der Isoenzyme in vitro fällt die kataly tische Aktivität exporientiell ab. Daran gekoppelt ist eine kontinuierliche Zunahme der Aktivierungsenergie, die errechnete Enzymmenge bleibt dabei konstant. Die Inaktiviefung verläuft demnach nicht nach dem Alles-oder-Niehts Prinzip, vielmehr muß eine stufenweise Inaktivierung der einzelnen Moleküle angenommen werden. Die Ergebnisse dieser Alterungsversuche, sowie Beobachtungen anderer Autoren lasseh vermuten, daß auch in vivo eine vergleichbare Inaktivierung stattfindet. l ) Nonstandard abbreviations: CK: creatine kinase (ATP: creatine-phosphotransferase, EC 2.7.3.2). Greatine kinase MM, MB and BB: creatine kinase isoenzymes from striated muscle, heart and brain, respectively.

SummaryThe apparent activation energy of the CK reaction as well as the Michaelis-Menten constants and the isoelectric point of CK MM can be used as indices for the mean age of the CK M-chain in the blood in vivo and in vitro. Modifications in the CK M-chain take place in vivo in the blood and in vitro in a serum matrix. Gradual increases in the apparent activation energy are also observed both in vivo and in vitro. It is confirmed that the modification in the CK M-chain causes a rise in the apparent activation energy, u.A gradual increase in apparent activation energy, due to the ageing process of the CK M-chain, was observed after myocardial infarction. A significantly increased value for u was observed at the time that total CK activity already had returned to reference values. In spite of the normal CK value, the apparent activation energy still indicated that there had been myocardial damage. The Michaelis-Menten constants for creatine phosphate and ADP are also influenced significantly by the modification in the M-chain. While the apparent activation energy increases, the Michaelis constants decrease in the order MM,, MM,, MM,. The Michaelis-Menten constants for both ADP and CrP can be used as an index for the mean age of the enzyme in the blood.The Michaelis-Menten constants for CrP and ADP show significant variations with the measuring temperature for virtually all CK MM forms.

Polyethylene-based water-and bone-equivalent plastics for Calibration phantoms in quantitative computed tomography (QCT) were optimized by calculation and experimental verification A composition of 91.3 % polyethylene, 5.5 % CaCO 3 , and 3.2 % MgO (by weight) was accepted äs being water-equivalent with respect to absolute value and energy dependence of the X-ray attenuation coeff icient; the material was compared to other commercially available solids. Boneequivalent samples containing 200 mg of hydroxyapatite per ml were obtained by adding the mineral powder to the water-equivalent material. A procedure for industrial mass production of both materials was developed. A first application of these materials is given by a new QCT Calibration phantom. Schlüsselwörter: Hydroxylapatit, Kalibrierung, Knochen, Mineralsalzbestimmung, Polyäthylen, Phantom, quantitative Computertomographie Durch Berechnung und experimentelle Untersuchungen wurde ein Eichphantom für die quantitative Computertomographie optimiert. Es handelt sich um einen festen Körper, dessen Grundmaterial Polyäthylen ist, aus welchem ein wasser-und knochenäquivalentes Material hergestellt wurde. Eine Mischung aus 91,3% (Gewichtsprozent) Polyäthylen, 5,5% CaCO 3 und 3,2 % MgO wurde für das wasseräquivalente Material verwendet. Die Übereinstimmung mit Wasser bezieht sich sowohl auf den absoluten Schwächungswert als auch auf dessen Abhängigkeit von der Energie der Röntgenstrahlen. Das Material wurde mit anderen kommerziell erhältlichen verglichen. Für die Knochenäquivalenz wurde dem Grundmaterial 200 mg Hydroxylapatit pro ml beigemischt. Zur industriellen Herstellung wurde ein Produktionsprozeß entwickelt, der hohe Homogenität garantiert. Das Material findet Verwendung in einem neuen QCT-Kalibrierphantom. IndroductionWater-and tissue-equivalent materials were first proposed and developed for radiation dosimetry purposes [11]. Equivalence of a synthetic material to a tissue or material of interest is assumed if the attenuation or energy absorption characteristics of the two respective materials are the same for a defined type of radiation. In the context of this paper, we will consider the equivalence of materials with respect to the linear X-ray attenuation coeff icient// over the energy ränge of 30 to 150 keV which is relevant to diagnostic X-ray procedures. The aim was to obtain calibration materials for QCT. Calibration phantom techniques for QCT, äs introduced by Genant and Cann, serve to control apparatus stability and to provide a calibration surve for conversion of CT numbers, measured in Hounsfield units (HU) f into bone mineral density (BMD) values, specified in mg/cm 3 [1]. The Cann/Gcnant phantom, developed for verlebral bone mineral measurement, consists of a perspex body containing bore holes filled with aqueous Solutions of ^HPO-t. Concern about the long-term stability of these Solutions gave rise to other groups' investigations [7,8,9] and to our efforts regarding the development of solid materials.The particular requirements for our work were t...

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