T cell receptor binding kinetics and special role of Valpha in T cell development and activation.

The kinetics of the interaction between T cell receptor (TCR) and major histocompatibility complex (MHC) has an important role in determining thymocyte-positive and -negative selection in the thymus, as well as in T cell activation. The alpha chain of the TCR is the major player in determining how the TCR fits onto the MHC ligand, and thus has a major role in determining whether a T cell develops as class I or class II restricted. In this article, we summarize recent data from our laboratory and others on the role of polymorphism in the Valpha combining site in determining MHC class restriction, and on kinetic parameters in thymocyte selection.

Selective spectrophotometric determination of glucose and fructose in the presence of aldoses using phenol-acetone reagent and cerium(III) chloride.

Aqueous mixtures of glucose and fructose produce red solutions when treated with 2% (w/v) phenol in 5% (v/v) aqueous acetone in the presence of concentrated sulfuric acid. The color is stable for days, and the red chromophore has an absorbance maximum at 568 nm. When the concentration of phenol is raised to 25%, fructose, but not glucose, produces red solutions, allowing for the selective detection of ketoses. Two complementary methods have been developed to remove the interference of ketoses in solutions containing glucose. The first one relies on the selective reduction of ketoses with sodium borohydride in the presence of cerium(III) chloride prior to the addition of the phenol-acetone reagents. The second method is based on the differential specific determination of glucose using 2% versus 25% levels of phenol. The relative sensitivities of different sugars are also presented as well as the applicability of the methods using bacterial polysaccharides for immunochemical analyses. The quantitative determination of glucose or ketoses in the polysaccharides does not require hydrolysis prior to the estimation.