tisone and of adrenocorticotropic hormone (ACTH) on
rheumatoid arthritis with Philip S. Hench, H. F. Polley,
and C. H. Slocumb. Kendall and Hench, along with
Tadeus Reichstein, shared the Nobel Prize in physiol-
ogy or medicine in 1950 for this work. Kendall
received many awards and honors. He died on May 4,
1972.
keratin A tough, insoluble, fibrous protein with high
sulfur content that forms the main structure and pro-
tective barrier or cytoskeleton of epidermal cells and is
the chief constituent of skin, hair and nails, and enamel
of the teeth. It is produced by keratinocytes, the most
abundant cells in the epidermis (95 percent). Keratin
makes up 30 percent of the cellular protein of all living
epidermal cells. The high amount of sulfur content is
due to the presence of the amino acid cystine.
ketone Organic compound in which a carbonyl
group is bound to two carbon atoms.
kilocalorie (kcal) One kilocalorie is equal to 1,000
calories, which is based on the amount of heat energy
required to raise the temperature of 1 kilogram of
water by 1°C; used to measure the energy value in food
and labor. Usually just called calorie; 1 kilocalorie
(kcal) = 1 Calorie (Cal) = 1,000 calories (cal). However,
in the International System of Units (ISU), the universal
unit of energy is the joule (J). One kilocalorie = 4.184
kilojoules (kJ).
kilogram The basic unit of mass (not of weight or of
force). A kilogram is equal to the mass of 1.000028
cubic decimeters of water at the temperature of its
maximum density.
kinetic ambiguity SeeKINETIC EQUIVALENCE.
kinetic control (of product composition) The
term characterizes conditions (including reaction times)
that lead to reaction products in a proportion governed
by the relative rates of the parallel (forward) reactions
in which the products are formed, rather than by the
respective overall equilibrium constants.
See alsoTHERMODYNAMIC CONTROL.kinetic electrolyte effect(kinetic ionic-strength
effect) The general effect of an added electrolyte (i.e.,
an effect other than, or in addition to, that due to its
possible involvement as a reactant or catalyst) on the
observed RATE CONSTANTof a reaction in solution. At
low concentrations (when only long-range coulombic
forces need to be considered), the effect on a given
reaction is determined only by the IONIC STRENGTHof
the solution and not by the chemical identity of the
ions. For practical purposes, this concentration range is
roughly the same as the region of validity of the Debye-
Hückel limiting law for activity coefficients. At higher
concentrations, the effect of an added electrolyte
depends also on the chemical identity of the ions. Such
specific action can usually be interpreted as the incur-
sion of a REACTION PATHinvolving an ion of the elec-
trolyte as reactant or catalyst, in which case the action
should not be regarded as simply a kinetic electrolyte
effect.
Kinetic electrolyte effects are usually (too restric-
tively and therefore incorrectly) referred to as “kinetic
salt effects.”
A kinetic electrolyte effect ascribable solely to the
influence of the ionic strength on activity coefficients of
ionic reactants and transition states is called a “pri-
mary kinetic electrolyte effect.” A kinetic electrolyte
effect arising from the influence of the ionic strength of
the solution upon the PRE-EQUILIBRIUMconcentration
of an ionic species that is involved in a subsequent
RATE-LIMITING STEPof a reaction is called a “secondary
kinetic electrolyte effect.” A common case encountered
in practice is the effect on the concentration of a hydro-
gen ion (acting as catalyst) produced from the IONIZA-
TIONof a weak acid in a buffer solution.
See alsoCOMMON-ION EFFECT; ORDER OF REAC-
TION.kinetic energy Energy of motion; kinetic energy
depends on the object’s mass and velocity and can be
described mathematically as K.E. =^1 / 2 mv^2. Moving
matter, be it a rolling rock, flowing water, or falling
ball, transfers a portion of its kinetic energy to other154 keratin