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Related Concept Videos

Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

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Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
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Nuclear Stability03:18

Nuclear Stability

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Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10−15 meters, a nucleus is quite small compared to the radius of the entire atom, which is about 10−10 meters. Nuclei are extremely dense compared to bulk matter, averaging 1.8 × 1014 grams per cubic centimeter. If the earth’s density were equal to the average nuclear density, the earth’s radius would be only about 200 meters.
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Mass Spectrometry: Isotope Effect01:13

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Most elements exist in nature as a mixture of isotopes. The isotopes differ in weight due to their respective number of neutrons. The molecular weight of a molecule is different depending on the specific isotope of its elements involved. As a result, the mass spectrum of the molecule exhibits peaks from the same fragment at multiple positions. The positions of these mass signals depend on the mass differences between isotopes. Furthermore, the intensity of these signals is dependent on the...
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Radioactivity and Nuclear Equations

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Nuclear chemistry is the study of reactions that involve changes in nuclear structure. The nucleus of an atom is composed of protons and, except for hydrogen, neutrons. The number of protons in the nucleus is called the atomic number (Z) of the element, and the sum of the number of protons and the number of neutrons is the mass number (A). Atoms with the same atomic number but different mass numbers are isotopes of the same element.
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In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis.
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Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

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NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of one, the...
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The Transition-State Structure for Human MAT2A from Isotope Effects.

Ross S Firestone1, Vern L Schramm1

  • 1Department of Biochemistry, Albert Einstein College of Medicine , 1300 Morris Park Avenue, Bronx, New York, New York 10461, United States.

Journal of the American Chemical Society
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Methionine adenosyltransferase II alpha (MAT2A) is a cancer target. Researchers elucidated its advanced SN2 transition state structure using kinetic isotope effects and quantum mechanics.

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Area of Science:

  • Biochemistry
  • Enzymology
  • Chemical Biology

Background:

  • Methionine adenosyltransferase II alpha (MAT2A) is a key enzyme in S-adenosylmethionine (SAM) synthesis.
  • MAT2A is an anticancer target in tumors deficient in 5'-methylthioadenosine phosphorylase (MTAP).
  • MTAP deficiency occurs in ~15% of human cancers and can be induced in others via inhibitors.

Purpose of the Study:

  • To determine the transition state structure of human MAT2A.
  • To investigate the effect of the MAT2B regulatory subunit on the MAT2A transition state.
  • To compare the MAT2A transition state with that of its bacterial homolog.

Main Methods:

  • Kinetic isotope effect (KIE) measurements.
  • Commitment factor (Cf) and binding isotope effect (BIE) analyses.
  • Quantum mechanical (QM) calculations.

Main Results:

  • The human MAT2A reaction proceeds via an advanced SN2 transition state.
  • Key bond distances and orders at the transition state were determined.
  • The MAT2B regulatory subunit did not alter the intrinsic KIEs or transition state structure.
  • The MAT2A transition state is more product-like than that of E. coli methionine adenosyltransferase.

Conclusions:

  • The study provides detailed insights into the catalytic mechanism of human MAT2A.
  • Understanding the MAT2A transition state can aid in the design of targeted anticancer therapies.
  • The regulatory subunit MAT2B does not influence the intrinsic catalytic mechanism of MAT2A.