Purification and Characterization of Kynurenine Aminotransferase I from Human Brain

Abstract: Two kynurenine aminotransferases (KATs), arbitrarily termed KAT I and KAT II, are capable of producing the neuroinhibitory brain metabolite kynurenic acid from l -kynurenine in human brain tissue. Here we describe the purification of KAT I to homogeneity and the subsequent characterization of the enzyme using physicochemical, biochemical, and immunological methods. KAT I was purified from human brain ∼2,000-fold with a yield of 2%. Assessed by polyacrylamide gel electrophoresis, KAT I migrated toward the anode as a single protein with a mobility of 0.5. The pure enzyme was found to be a dimer consisting of two identical subunits of ∼60 kDa. Among several oxo acids tested, KAT I showed highest activity with 2-oxoisocaproate. Kinetic analyses of the pure enzyme revealed an absolute K _m of 2.0 m M and 10.0 m M for l -kynurenine and pyruvate, respectively. KAT I activity was substantially inhibited by l -glutamine, l -phenylalanine, and l -tryptophan, using either pyruvate (1 m M ) or 2-oxoisocaproate (1 m M ) as a cosubstrate. l -Tryptophan inhibited enzyme activity noncompetitively with regard to pyruvate ( K _i = 480 µ M ) and competitively with regard to l -kynurenine ( K _i = 200 µ M ). Anti-KAT I antibodies were produced against pure KAT I and were partially purified by conventional techniques. Immunotitration and immunoblotting analyses confirmed that KAT I is clearly distinct from both human KAT II and rat kynurenine-pyruvate aminotransferase. Pure human KAT I and its antibody will serve as valuable tools in future studies of kynurenic acid production in the human brain under physiological and pathological conditions.     

Changes in the Shape and Surface Hydrophobicity of Ovalbumin during Its Transformation to S-Ovalbumin

Intrinsic viscosity, Stokes radius and the hydrophobic coefficient of Keshavarz and Nakai [Biochim. Biophys. Acta, 576, 269 (1979)] were measured to compare the shape and surface hydrophobicity of ovalbumin and s-ovalbumin. Both the intrinsic viscosity and Stokes radius of s- ovalbumin were smaller than those of ovalbumin, which suggests that the configuration of s- ovalbumin became more compact during the ovalbumin-s-ovalbumin transformation. The hydrophobic coefficient of s-ovalbumin was larger than that of ovalbumin, which suggests that the surface hydrophobicity of s-ovalbumin was larger than that of ovalbumin. Further, these properties were measured for ovalbumin samples obtained at various stages of ovalbumin-s-ovalbumin transformation. Changes in the shape and surface hydrophobicity of ovalbumin were not found in the first stage of ovalbumin-s-ovalbumin transformation. They changed rapidly in the last stage of the ovalbumin-s-ovalbumin transformation.     

Effects of different light intensities during the forenoon on the afternoon thermal sensation in mild cold

1. 1. The study aimed at knowing whether thermal sensation during afternoon cool exposure could be influenced by bright light (4000 lx) or dim light (200 lx) in the forenoon.

2. 2. The subjects felt cooler after exposure to dim light than to bright light.

3. 3. Melatonin in the urine was significantly higher in bright light than in dim light at 10:30 h and at noon.

     

Studies on the Foaming Property of the Chicken Egg White

The egg white was treated under various whipping conditions, and its foaminess measured. At the same time, the amounts of the coagulated proteins formed from each egg white and their constituent hexose were measured. From these results, discussions were made about the relation between the foaminess of the egg white and the amount of the coagulated proteins under various whipping conditions.     

Response Variance in Functional Maps: Neural Darwinism Revisited

The mechanisms by which functional maps and map plasticity contribute to cortical computation remain controversial. Recent studies have revisited the theory of neural Darwinism to interpret the learning-induced map plasticity and neuronal heterogeneity observed in the cortex. Here, we hypothesize that the Darwinian principle provides a substrate to explain the relationship between neuron heterogeneity and cortical functional maps. We demonstrate in the rat auditory cortex that the degree of response variance is closely correlated with the size of its representational area. Further, we show that the response variance within a given population is altered through training. These results suggest that larger representational areas may help to accommodate heterogeneous populations of neurons. Thus, functional maps and map plasticity are likely to play essential roles in Darwinian computation, serving as effective, but not absolutely necessary, structures to generate diverse response properties within a neural population.