Hiroshi Shiraki

Interaction of rat muscle AMP deaminase with myosin: I. Biochemical study of the interaction of AMP deaminase and myosin in rat muscle

AMP deaminase was completely solubilized from rat skeletal muscle with 50 mM Tris-HCl buffer (pH 7.0) containing KCl at a concentration of 0.3 M or more. The purified enzyme was found to be bound to rat muscle myosin or actomyosin, but not to F-actin at KCl concentrations of less than 0.3 M. Kinetic analysis indicated that 1 mol of AMP deaminase was bound to 3 mol of myosin and that the dissociation constant (Kd) of this binding was 0.06 micrometer. It was also shown that AMP deaminase from muscle interacted mainly with the light meromyosin portion of the myosin molecule. This finding differs from that of Ashby and coworkers on rabbit muscle AMP deaminase, probably due to a difference in the properties of rat and rabbit muscle AMP deaminase. AMP deaminase isozymes from rat liver, kidney and cardiac muscle did not interact with rat muscle myosin. The physiological significance of this binding of AMP deaminase to myosin is discussed.

Adenylosuccinate synthetase in rat liver: the existence of two types and their regulatory roles.

Abstract Rat liver contains two types of adenylosuccinate synthetase which can be distinguished by isoelectroforcusing or immunochemical analysis. One type is identical with the enzyme in rat skeletal muscle (Type M) and the other is specific for the liver (Type L). Type L was more susceptible to nucleotide inhibition, but less susceptible to inhibition by fructose-1,6-diphosphate than Type M. These differences suggest that these isozymes play different regulatory roles in the liver.

Interaction of rat muscle AMP deaminase with myosin: II. Modification of the kinetic and regulatory properties of rat muscle AMP deaminase by myosin

The problems of whether the kinetic and regulatory properties of AMP deaminase were modified by formation of a deaminase-myosin complex were investigated with an enzyme preparation from rat skeletal muscle. Results showed that AMP deaminase was activated by binding to myosin. Myosin-bound AMP deaminase showed a sigmoidal activity curve with respect to AMP concentration in the absence of ATP and ADP, but a hyperbolic curve in their presence. Addition of ATP and ADP doubled the V value, but did not affect the Km value. Myosin-bound AMP deaminase also gave a sigmoidal curve in the presence of alkali metal ions, whereas free AMP deaminase gave a hyperbolic curve. GTP abolished the activating effects of both myosin and ATP.

Study on the regulatory role of fructose-1,6-diphosphate in the formation of AMP in rat skeletal muscle. A mechanism for synchronization of glycolysis and the purine nucleotide cycle.

Abstract Fructose-1,6-diphosphate strongly inhibited adenylosuccinate synthetase purified from rat skeletal muscle. This compound was found to be a non-competitive inhibitor of all substrates of the enzyme. No other glycolytic intermediates affected adenylosuccinate synthetase activity. From these findings, it was proposed that this inhibition might play an important role in the oscillation of glycolysis in skeletal muscle.

Possible correlation between binding of muscle type AMP deaminase to myofibrils and ammoniagenesis in rat skeletal muscle on electrical stimulation

Abstract Contraction of rat skeletal muscle by electrical stimulation of the sciatic nerve caused remarkable increase in binding of AMP deaminase (EC 3.5.4.6) to myofibrils, but did not change the total enzyme activity. After 30 sec stimulation, the ratio of bound to free enzyme was about 5 times that in resting muscle. This treatment also increased the ammonia content of the muscle to 5 times that in resting state. From these findings, we suggest that there is a correlation between the binding of muscle type AMP deaminase to myofibrils and ammoniagenesis in the muscle.

Purification and properties of adenylosuccinate synthetase from Yoshida sarcoma ascites tumor cells

Adenylosuccinate synthetase (IMP:L-aspartate ligase (GDP-forming), EC 6.3.4.4) was purified about 750-fold to a homogeneous state from Yoshida sarcoma ascites tumor cells. A yield of 38% purified enzyme was achieved by a procedure including affinity chromatography on hadacidin-Sepharose 4B. Ultracentrifugal analyses showed that the molecular weight of the native enzyme was 102 000 with an s20,w value of 4.5 and that the molecular weight in 6 M guanidine-HCl was 47 000. These values indicate that the native enzyme is composed of two subunits. The isoelectric point was determined to be 5.9 by isoelectric focusing. The optimum pH for activity was 6.8-7.0. The Km values for IMP, aspartate and GTP were calculated to be 4.1, 9.8 and 0.7 . 10(-4) M, respectively. The antibiotic, hadacidin was strongly inhibitory, causing competitive inhibition with respect to aspartate with a Ki value of 2.5 . 10(-6) M. Nucleoside mono- and diphosphate also inhibited the enzyme activity, but their inhibitions were not apparently specific. The purified enzyme showed full activity in the presence of Mg2+, and Mg2+ could be partially replaced by Mn2+, Co2+, Ca2+ or Cu2+. Divalent metal ions, such as Cd2+, Pb2+, Zn2+, Cu2+ and Mn2+, interfered with the activity by antagonizing Mg2+. Hg2+ or PCMB inactivated the enzyme, suggesting that an SH-group may be important for activity.

Purification and characterization of adenylate kinase isozymes from rat muscle and liver

Isozymes of adenylate kinase (ATP:AMP phosphotransferase, EC 2.7.4.3) were purified from skeletal muscle and liver of rats to essentially homogeneous states by acrylamide gel electrophoresis and sodium dodecyl sulfate gel electrophoresis. The isozyme from muscle was purified by acidification to pH 5.0, and column chromatography on phosphocellulose, Sephadex G-75 and Blue Sepharose CL-6B, while that from liver was purified by column chromatography on Blue Sepharose CL-6B, Sephadex G-75 and carboxymethyl cellulose. By these procedures the muscle isozyme was purified about 530-fold in 29% yield, and the liver isozyme about 3600-fold in 27% yield from the respective tissue extracts. The molecular weights of the muscle and liver isozymes were estimated as about 23 500 and 30 500, respectively, by both sodium dodecyl sulfate gel electrophoresis and molecular sieve chromatography, and no subunit of either isozyme was detected. The isoelectric points of the muscle and liver isozymes were 7.0 and 8.1, respectively. The Km values of the respective enzymes for ATP and ADP were similar, but the Km(AMP) of the liver isozyme was about one-fifth of that of the muscle isozyme. Immunological studies with rabbit antiserum against the rat muscle isozyme showed that the muscle isozyme was abundant in muscle, heart and brain, while the liver isozyme was abundant in liver and kidney.

Change in content of adenylossucinate synthetase isozymes during liver regeneration in rats

Abstract The distribution of adenylosuccinate synthetase isozymes changed during liver regeneration in the rat. Type L enzyme increased in correlation with liver cell proliferation and reached a maximum of approximately 80% of total activity, whereas Type M enzyme decreased conversely. These findings suggest that Type L enzyme in liver contributes to adenine nucleotide biosynthesis.

Increase in nucleoside diphosphatase in rat brain striatum lesioned with kainic acid.

The activity of ammoniagenesis from guanine nucleotides was found to increase significantly in rat brain after infusion of kainic acid into the striatum. Among the enzymes involved in degrading guanine nucleotides, nucleoside diphosphatase was markedly increased in the lesioned striatum. The enzyme activity began to increase 2 days after the infusion, and reached the maximum on the 13th day, the level being 4 times as high as that of the intact contralateral region. The increased activity was due to Type L enzyme, judging from its substrate specificity. Puromycin and cycloheximide inhibited this increase, indicating that the increased activity resulted from an increase in the net synthesis of the enzyme. These findings suggest that Type L NDPase might play some important roles in gliosis after neuronal lesion.

Preliminary crystallographic data for adenylosuccinate synthetase from rabbit skeletal muscle.

Abstract Single crystals of adenylosuccinate synthetase, an essential component of purine biosynthesis, extracted from rabbit skeletal muscle were prepared as suitable specimens for X-ray structure analysis. The crystal belongs to the space group P 4 3 2 1 2 or P 4 1 2 1 2 with unit cell dimensions a = b = 71.2 A , c = 194.8 A . The asymmetric unit contains one protein molecule of 54,000 molecular weight.