isoelectric point

Also found in: Dictionary, Thesaurus, Legal, Financial, Acronyms, Encyclopedia, Wikipedia.


1. a small area or spot; the sharp end of an object.
2. to approach the surface, like the pus of an abscess, at a definite spot or place.
3. a tapered, pointed endodontic instrument used for exploring the depth of the root canal in root canal therapy; called also root canal point.
point A a radiographic, cephalometric landmark, determined on the lateral head film; it is the most retruded part of the curved bony outline from the anterior nasal spine to the crest of the maxillary alveolar process.
absorbent point in root canal therapy, a cone of variable width and taper, usually made of paper or a paper product, used to dry or maintain a liquid disinfectant in the canal. Called also paper point.
point B a radiographic, cephalometric landmark, determined on the lateral head film; it is the most posterior midline point in the concavity between the infradentale and pogonion.
boiling point the temperature at which a liquid will boil; at sea level the boiling point of water is 100°C (212°F).
cardinal p's
1. the points on the different refracting media of the eye that determine the direction of the entering or emerging light rays.
2. four points within the pelvic inlet— the two sacroiliac articulations and the two iliopectineal eminences.
craniometric p's the established points of reference for measurement of the skull.
dew point the temperature at which moisture in the atmosphere is deposited as dew.
far point the most remote point at which an object is clearly seen when the eye is at rest.
point of fixation
1. the point or object on which one's sight is fixed and through which the axis opticus passes.
2. the point on the retina, usually the fovea, on which are focused the rays coming from an object directly regarded.
freezing point the temperature at which a liquid begins to freeze, for water, 0°C (32°F); it is often used interchangeably with melting point, but should be used for substances being cooled while melting point is reserved for substances being heated.
gutta-percha point gutta-percha cone.
ice point the true melting point of ice, being the temperature of equilibrium between ice and air-saturated water under one atmosphere pressure.
isoelectric point (pI) the pH of a solution in which molecules of a specific substance, such as a protein, have equal numbers of positively and negatively charged groups and therefore do not migrate in an electric field.
J point on an electrocardiogram, the junction between the end of the QRS segment and the beginning of the ST segment.
jugal point the point at the angle formed by the masseteric and maxillary edges of the zygomatic bone; called also jugale.
lacrimal point a small aperture on a slight elevation at the medial end of the eyelid margin, through which tears from the lacrimal lake enter the lacrimal canaliculi. See also lacrimal apparatus.
point of maximal impulse the point on the chest where the impulse of the left ventricle is sometimes felt or seen most strongly, normally in the fifth costal interspace inside the mammillary line.
McBurney point a point of special tenderness in appendicitis, about 4 to 5 cm from the right anterior iliac spine on a line between the spine and the navel; it corresponds to the normal position of the appendix.
McBurney's point is located midway between the anterior iliac crest and the umbilicus in the right lower quadrant. From Ignatavicius and Workman, 2002.
melting point (mp) the minimum temperature at which a solid begins to liquefy; see also freezing point.
near point the nearest point of clear vision, the absolute near point being that for either eye alone with accommodation relaxed, and the relative near point being that for the two eyes together with employment of accommodation.
nodal p's two points on the axis of an optical system situated so that a ray falling on one will produce a parallel ray emerging through the other.
paper point absorbent point.
pressure point
1. a point of extreme sensitivity to pressure.
2. one of various locations on the body at which digital pressure may be applied for the control of hemorrhage.
Locations of pressure points. Shaded areas show the regions in which hemorrhage may be controlled by pressure at the points indicated.
root canal point point (def. 3).
silver point in root canal therapy, a tapered and elongated silver plug that is cemented into the canal as a filling. Called also silver cone.
trigger point a spot on the body at which pressure or other stimulus gives rise to specific sensations or symptoms.
triple point the temperature and pressure at which the solid, liquid, and gas phases of a substance are in equilibrium.

i·so·e·lec·tric point (pI, IEP, IP),

the pH at which an amphoteric substance, such as protein or an amino acid, is electrically neutral.

isoelectric point

the pH at which a molecule containing two or more ionizable groups is electrically neutral. The average number of positive charges equals the average number of negative charges.

i·so·e·lec·tric point

(pI) (ī'sō-ĕ-lek'trik poynt)
The pH at which an amphoteric substance, such as protein or an amino acid, is electrically neutral.

isoelectric point (IEP, pI)

the PH of an AMPHOTERIC solution when at electrical neutrality, the ionic state of an AMINO ACID at the isoelectric point being a ZWITTERION. For each amino acid there is a characteristic pH value for a solution in which the tendency to ionize as a base is balanced by the tendency to ionize as an acid. At this pH the amino acid thus behaves as neither an anion nor a cation, the net charge is zero and it does not migrate in an electric field. For individual proteins there is also a characteristic pH value at which the molecule is electrically neutral. At this point the solubility of the protein is less than at any other pH. Thus many proteins will precipitate out of solution at their isoelectric points. It is therefore generally desirable that proteins in cells and tissues are not at their isoelectric point. The isoelectric point of proteins can often be determined by e.g. finding the point of maximum turbidity in a series of solutions at various pHs. Proteins can be separated from mixtures by fractional precipitation using, for example, ammonium sulphate, with the pH of the solution adjusted to the isoelectric point of the protein.

iso·e·lec·tric point

(pI) (ī'sō-ĕ-lek'trik poynt)
The pH at which an amphoteric substance is electrically neutral.

isoelectric point,

n the pH at which a molecule containing two or more ionizable groups is electrically neutral.
References in periodicals archive ?
Both proteins are glycosylated, have similar amino acid compositions, and have isoelectric points of 4.
The molecular weight of most of these proteins ranged from 43 to 97kDa and the isoelectric points of these proteins ranged from 5 to 9.
In the results of the isoelectric points (pI), there were various values (4.
The isoelectric point of sesame protein was approximately pH 4.
protein separation by mass spectrometry followed by separation by isoelectric point followed by molecular weight.
The combination of dynamic and electrophoretic light scattering makes measurement of protein isoelectric point simple and precise.
Results of isoelectric focusing showed 3 isoelectric point values (5.
High levels of histidine sorption to the acid soil, in comparison to the calcareous soil, were probably related to the isoelectric point of histidine and to the difference of pH between the soils.
While studying Moringa proteins we identified and isolated a specific protein fraction whose molecular weight is relatively low, 6,000-13,000 daltons, and whose isoelectric point is 10, so that it is cationic.
There are several isoforms of carboxylesterases that have been classified based on substrate specificity and their isoelectric point (26).
The calculated molecular weight of the deduced primary sequence is 49 kDa, with a predicted isoelectric point of 5.