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H+: the hydrogen ion, proton.
H2S04-Na2S04 buffer: a system of buffer solution containing varying ratios of sulfuric acid and its salt, sodium sulfate, maintains stable pH between neutral to as low as 1.3.
half-life: the time required for half of something to undergo a process, like that in the decay of radioactivity of an isotope.
Hammett's σ constant: an empirically determined set of constants, which describes the relative effectiveness of specific substituent on aromatic molecules in producing an inductive effect on a target functional group a distance away.
H-bond: hydrogen bond, a linkage consisting of a hydrogen atom bridging two electronegative atoms such as oxygen and nitrogen.
H-bonding partner: The imino group and the carbonyl group of a protein, for example, are H-bonding partners to one another in the H-bond formed between their respective nitrogen and oxygen atom.
HBr: hydrogen bromide, a colorless corrosive and noninflammable gas.
half time of exchange: the time needed for one half of the ions or molecules in one phase to exchange with similar ions and molecules in an adjoining space, usually determined with the use
of radioactively labeled isotopes.
HDO: deuteriated water, heavy water Water in which one of the hydrogen atoms has been replaced by its isotope, deuterium.
heat of dephosphorylation: the amount of heat evolved when I gram mole of a phosphate-containing compound such as ATP is dephosphorylated.
heat of neutralization: the amount of heat evolved when one gram mole of an acid or base is neutralized at constant temperature and pressure.
heat content change, enthalpy change, ΔH: the change in the heat content or enthalpy, which equals the internal energy of a body plus the product of its volume and pressure heat-activated cellulose acetate membrane: See cellulose acetate membrane.
Helmholtz free energy, work function, A: a thermodynamic function defined by A = E
- TS, where E is the energy or internal energy, Т and S are the absolute temperature and entropy respectively It represents the maximum work that can be made available in a given isothermal process. Note that free energy, or Gibbs free energy represented as F and work function or Helmholtz free energy represented as A are different by the relation F
= A + PV. Since most cell physiological activities occur in solution where there is little change in volume or pressure, changes in Gibbs free energy and Helmholtz free energy are to all intents and purposes the same. (See also free energy.)
heme: the deep red, iron-containing prosthetic group of hemoglobin.
heme site: Each hemoglobin molecule contains 4 heme groups. Since each heme can bind one oxygen molecule during the oxygenated state, each heme on a hemoglobin molecule offers a binding site for oxygen and is sometimes referred to as a heme site.
hemoglobin: the pigment-protein complex of red blood cells by means of which these cells are able to transport oxygen from the lungs to the body tissues Each hemoglobin molecule comprises 4 subunits: two called a-chains and two called P-chains.
hemolysis: lysis of red blood cells with liberation of hemoglobin.
Henry's Law: At constant temperature, the mass of gas dissolved by a given volume of solvent is proportional to the pressure of the gas with which it is in equilibrium. This law was introduced by W. Henry in 1803 and is a special case of the Berthelot-Nemst partition law.
heterocooperative interaction: cooperative interaction with a negative nearest-neighbor interaction energy or
-γ/2. For a system with two alternative adsorbents, i
and j, a hetero-cooperative interaction means that the adsorption of one species, i, enhances the adsorption of the alternative adsorbent, j. Heterocooperative interaction, a term introduced in the
AI Hypothesis, is equivalent to what is called antiferromagnetic cooperative interaction.
hexose: a monosaccharide like D-glucose that contains six carbon atoms in the molecule.
H3HO: tritiated water, in which one of the hydrogen atoms of a water molecule has been replaced by the radioactive tritium atom. Tritiated water is of great value in the study of movement of molecular water in living systems.
high energy phosphate bond: the concept that certain organic phosphate compounds like ATP contain extra amount of utilizable free energy (-12 to -16 Kcal /mole) in its phosphate bonds that can be tapped to perform biological work In 1956 Podolsky and Morales demonstrated that the enthalpy of the
ATP phosphate bond is only -4.7 Kcal/mole and thus not different from what has been called low energy phosphate bonds like that in AMP.
high negative energy: See negative energy.
high (negative) energy-low entropy state: In the AI Hypothesis, the living cell and protoplasm may exist in a resting living state, in which the total negative energy is high and the total entropy is low. This state is thus referred to as high (negative) energy-low entropy state.
Hill coefficient, n: an empirically determined constant represented by the letter, n, introduced by A.V. Hill to measure the "sigmoidity" of the oxygen binding curve of hemoglobin In 1964, Ling
demonstrated488 that n in fact equals - exp (γ/2kT), where
-γ/2 is the nearest neighbor interaction energy of an autocooperative phenomenon, k is the Boltzmann constant and T, the absolute temperature.
histidine: a basic a-amino acid found in most protein hydrolysates.
Hodgkin-Huxley theory of action potential: a theory of the nerve and muscle action potential introduced by British physiologists A. L. Hodgkin and A. Huxley. Based on the membrane-pump theory, this theory postulates the sequential opening and closing of specific
Na+ and K+ channels as the physical basis for the nerve or muscle impulse.
homogenate: a ground up paste.
hormone: a chemical substance secreted into the body fluids by an endocrine gland, which has a specific effect on the activity of other organs.
Hsiung-nu: The word nu means slaves. Hsiung-nu is the deprecatory name used by ancient Chinese against northern tribes. Hsiung-nu thus really means Hun-slaves, since the word Hsiung is also pronounced Hun. Witness the Chinese word chosen to represent the first syllable of the word, Hungary, is also Hsiung (pronounced as Hun).
Huns: same as Hsiung-nu, a collective name for northern Mongolian tribes. After being defeated by Han soldiers, part of these tribes moved west. As time went by, they grew stronger. Around 450 AD they took control of large part of central Asia and Europe under their able leader, Attila.
hydrated ion: In water, alkali-metal ions like K+ are surrounded by a more or less permanent layer(s) of hydration water and are called hydrated ions.
hydrated K+, hydrated Na+: See hydrated ion.
hydration water: water molecules attached more-or-less permanently to ions, nonelectrolytes, macromolecules including proteins, etc. See hydrated ion.
hydrogen bond: See H-bond.
hyperbola: a plane curve generated by a point so moving that the difference of the distances from two fixed points is a constant.
hyperbolic: of, or relating to a hyperbola.
"hyperbolic" curve: It is an age-honored tradition to describe a plot of the rate of enzyme reaction (y) as ordinate against the substrate concentration (x) as abscissa where у rises sharply initially at low x, slowing down steadily thereafter at increasing x [and other similar plots like the oxygen uptake curve of myoglobin (See left curve in Inset of Fig. 55.)] as representing part of a rectangular hyperbola and thus hyperbolic. This is an approximate but inexact description. In a rectangular Cartesian x-y plot, the equation describing a rectangular hyperbola is
x2 - y2 = a2, where a is a constant. The equations of the asymptotes are y = x and y = - x. In other words, y rises steadily with x as x approaches infinity. This is at odds with both the Henri-Michaelis-Menten equation of enzyme kinetics or Langmuir adsorption isotherm, in both of which y approaches a constant value as x approaches infinity. For this reason and in due respect for tradition, I have used the word hyperbolic from time to time but under quotation marks.
hyperpolarization: to produce an increase in the potential difference across (a cell surface).
hypertonic: at a concentration higher than that which would maintain living cells at their normal sizes.
hypotonic: at a concentration lower than that which would maintain living cells at their normal sizes.
hydroxyproline: a common α-amino acid found in some protein hydrolysate
like proline but unlike most other α-amino acids, when a hydroxyproline is incorporated into a polypeptide chain or protein, its pyrrolidine nitrogen no longer carries a hydrogen atom and is consequently unable to form an
α-helical or other inter- or intra-macromolecular H bond.
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