Enzyme is active tetramer
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Pyruvate carboxylase—55,000χ and 2,000,000χ Active tetramer, inactive subunits In explaining what happens to neu- rons, the Indiana chemist, who has just returned from a year's sabbatical at Queensland, points out that an elec- trical field exists across the cell mem- brane enclosing the neuron. Inside the membrane, there are about seven times as many potassium ions as there are sodium ions. The reverse holds true outside the membrane. When an impulse strikes the neuron, the permeability of the membrane changes. Sodium ions on the outside then move inside. This pulse of ions sets off a current down the nerve. The problem with this mechanism has been in explaining how such ap- parently small electrical forces can change the permeability of the neuron membrane. Dr. Moore points out that there is a 70-mv(e). potential across the neuron membrane. But this mem- brane is very thin, just 70 A. Hence the potential across the membrane cor- responds to a field of 10 5 volts per cm. The Wien effect indicates that the dissociation of an acid increases with the increasing strength of the electrical field containing the acid. Thus, by us- ing the theory of the Wien effect (de- veloped by Dr. Lars Onsager of Yale), and plugging in both the 10 5 volt-per- cm. field and the characteristics of the substituted phosphoric acids making up the membrane, Dr. Moore and his colleague have calculated that changes in membrane potential can increase the membrane pH by as much as 0.2. Earlier studies on the effects of var- ious solutions in neurons show that such a pH change is enough to alter the permeability of the membrane and trigger the pulse of sodium ions and the nerve impulse. The new theory is also consistent with extensive data on the effects of alkalosis on the nervous system, Dr. Moore adds. Mathematician Bass Membrane potential Enzyme is active tetramer Pyruvate carboxylase, an enzyme from chicken liver mitochondria, exists as an active tetramer at 23° C, but as four nearly equal dissociated subunits in its deactivated state at 2° C, according to chemists at London's National Institute for Medi- cal Research, Mill Hill, and Western Reserve University, Cleveland, Ohio [Biochemistry, 5, 3111 (1966)]. Pyruvate carboxylase is an enzyme which has been proposed to catalyze the first step in the synthesis of gly- cogen from pyruvate in liver. The Mill Hill group used electron microscopy and the Western Reserve group used sedimentation techniques. The enzyme was examined in both the catalytically activated and deacti- vated states. The Mill Hill group prepared the deactivated enzyme by incubation of pyruvate carboxylase at 2° C. using a method developed by Dr. Milton Utter, Dr. Michael C. Scrutton, and Dr. Julian Irias of West- ern Reserve. After the incubation, the enzyme was examined in the elec- tron miscroscope by Dr. Robin C. Valentine and Nicholas G. Wrigley. The enzyme was then reactivated by warming it to 23° C. Comparisons of the micrographs in- dicate that the reactivated enzyme and the original are quite similar. The active enzyme appears as four nearly equal spheres at the corners of a square. After inactivation, this tetrameric structure is no longer visi- ble. However, the tetrameric struc- ture returns after warming to 23° C. The estimated diameter of the sub- units is approximately the same (70 to 75 A.) as that which can be cal- culated from one fourth of the molec- ular weight derived from sedimenta- tion studies. Dr. Utter and Dr. Scrutton proposed earlier that each of the four subunits contains both biotin and manganese. Sedimentation studies of the deac- tivated enzyme indicate a molecular weight of 165,000, compared with a molecular weight of 660,000 for the original enzyme. The Western Reserve group pre- viously found that in the presence of 1% sodium dodecyl sulfate, pyruvate carboxylase dissociates to yield yet smaller subunits each having a molec- ular weight of about 45,000. These smaller subunits could not be re- solved under the electron microscope. Microwave institute starts up The International Microwave Power Institute (IMPI) officially got under way at a meeting in Palo Alto, Calif. The institute's aim is to further the use and understanding of microwave energy in areas other than information and communication. IMPI will go about this by sponsoring annual con- ferences, publishing the Journal of Microicave Power, and promoting re- search and development of microwave energy applications. Groundwork for the new institute was laid at a micro- wave conference in Edmonton, Alta., last March. Dr. W. A. Geoffrey Voss, 31, associ- ate professor of electrical engineering at the University of Edmonton, is IMPI's chairman. Microwave technology faces a promising, and lucrative, future. Mar- kets for microwave equipment could reach $500 million within the next 15 years, believes John E. Gerling, vice president of Litton Industry's Ather- ton division and IMPI's first president. Microwaves are part of the electro- magnetic spectrum. Like light waves, they pass through some materials and are reflected or absorbed by others. They are generated by radiofrequency power tubes from high-voltage direct current. Magnetron, amplitron, and klystron tubes are the most common. When microwaves pass through ma- terials such as food, wood, and plastic, the molecules within the material at- tempt to align themselves with the di- rection of the electrical field. As the molecules oscillate around their axes, they create intramolecular friction and produce heat. There's a fundamental difference be- tween heating a substance conven- tionally and heating it with micro- waves. In the first case, the outer OCT. 17, 1966 C&EN 37
Transcript of Enzyme is active tetramer
Pyruvate carboxylase—55,000χ and 2,000,000χ Active tetramer, inactive subunits
In explaining what happens to neurons, the Indiana chemist, who has just returned from a year's sabbatical at Queensland, points out that an electrical field exists across the cell membrane enclosing the neuron. Inside the membrane, there are about seven times as many potassium ions as there are sodium ions. The reverse holds true outside the membrane.
When an impulse strikes the neuron, the permeability of the membrane changes. Sodium ions on the outside then move inside. This pulse of ions sets off a current down the nerve.
The problem with this mechanism has been in explaining how such apparently small electrical forces can change the permeability of the neuron membrane. Dr. Moore points out that there is a 70-mv(e). potential across the neuron membrane. But this membrane is very thin, just 70 A. Hence the potential across the membrane corresponds to a field of 105 volts per cm.
The Wien effect indicates that the dissociation of an acid increases with the increasing strength of the electrical field containing the acid. Thus, by using the theory of the Wien effect (developed by Dr. Lars Onsager of Yale), and plugging in both the 105 volt-per-cm. field and the characteristics of the substituted phosphoric acids making up the membrane, Dr. Moore and his colleague have calculated that changes in membrane potential can increase the membrane pH by as much as 0.2.
Earlier studies on the effects of various solutions in neurons show that such a pH change is enough to alter the permeability of the membrane and trigger the pulse of sodium ions and the nerve impulse. The new theory is also consistent with extensive data on the effects of alkalosis on the nervous system, Dr. Moore adds.
Mathematician Bass Membrane potential
Enzyme is active tetramer Pyruvate carboxylase, an enzyme from chicken liver mitochondria, exists as an active tetramer at 23° C , but as four nearly equal dissociated subunits in its deactivated state at 2° C , according to chemists at London's National Institute for Medical Research, Mill Hill, and Western Reserve University, Cleveland, Ohio [Biochemistry, 5, 3111 (1966)]. Pyruvate carboxylase is an enzyme which has been proposed to catalyze the first step in the synthesis of glycogen from pyruvate in liver. The Mill Hill group used electron microscopy and the Western Reserve group used sedimentation techniques.
The enzyme was examined in both the catalytically activated and deactivated states. The Mill Hill group prepared the deactivated enzyme by incubation of pyruvate carboxylase at 2° C. using a method developed by Dr. Milton Utter, Dr. Michael C. Scrutton, and Dr. Julian Irias of Western Reserve. After the incubation, the enzyme was examined in the electron miscroscope by Dr. Robin C. Valentine and Nicholas G. Wrigley. The enzyme was then reactivated by warming it to 23° C.
Comparisons of the micrographs indicate that the reactivated enzyme and the original are quite similar. The active enzyme appears as four nearly equal spheres at the corners of a square. After inactivation, this tetrameric structure is no longer visible. However, the tetrameric structure returns after warming to 23° C.
The estimated diameter of the sub-units is approximately the same (70 to 75 A.) as that which can be calculated from one fourth of the molecular weight derived from sedimentation studies. Dr. Utter and Dr. Scrutton proposed earlier that each of the four subunits contains both biotin and manganese.
Sedimentation studies of the deactivated enzyme indicate a molecular weight of 165,000, compared with a molecular weight of 660,000 for the original enzyme.
The Western Reserve group pre
viously found that in the presence of 1% sodium dodecyl sulfate, pyruvate carboxylase dissociates to yield yet smaller subunits each having a molecular weight of about 45,000. These smaller subunits could not be resolved under the electron microscope.
Microwave institute starts up The International Microwave Power Institute (IMPI) officially got under way at a meeting in Palo Alto, Calif. The institute's aim is to further the use and understanding of microwave energy in areas other than information and communication. IMPI will go about this by sponsoring annual conferences, publishing the Journal of Microicave Power, and promoting research and development of microwave energy applications. Groundwork for the new institute was laid at a microwave conference in Edmonton, Alta., last March.
Dr. W. A. Geoffrey Voss, 31, associate professor of electrical engineering at the University of Edmonton, is IMPI's chairman.
Microwave technology faces a promising, and lucrative, future. Markets for microwave equipment could reach $500 million within the next 15 years, believes John E. Gerling, vice president of Litton Industry's Ather-ton division and IMPI's first president.
Microwaves are part of the electromagnetic spectrum. Like light waves, they pass through some materials and are reflected or absorbed by others. They are generated by radiofrequency power tubes from high-voltage direct current. Magnetron, amplitron, and klystron tubes are the most common.
When microwaves pass through materials such as food, wood, and plastic, the molecules within the material attempt to align themselves with the direction of the electrical field. As the molecules oscillate around their axes, they create intramolecular friction and produce heat.
There's a fundamental difference between heating a substance conventionally and heating it with microwaves. In the first case, the outer
OCT. 17, 1966 C&EN 37
