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Two kynurenine aminotransferases in human brain
E Okuno1, M Nakamura, R Schwarcz
1Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, 21228.
Brain Research
|March 1, 1991
Summary
Researchers identified two distinct human brain enzymes, kynurenic acid (KYNA) producers, using Tris-acetate buffer. These enzymes, KAT I and KAT II, differ in cofactor preference and pH optimum, impacting KYNA synthesis regulation.
Area of Science:
- Biochemistry
- Neuroscience
- Human Physiology
Background:
- Kynurenic acid (KYNA) is a neuroinhibitory metabolite in the human brain.
- Its synthesis from L-kynurenine is crucial for understanding neurological function.
- Conventional phosphate buffers obscured the presence of distinct KYNA-producing enzymes.
Purpose of the Study:
- To identify and characterize the enzymes responsible for kynurenic acid (KYNA) synthesis in human brain tissue.
- To differentiate between multiple forms of kynurenine aminotransferases (KATs).
- To investigate the distinct properties and potential regulatory roles of these enzymes.
Main Methods:
- Utilized Tris-acetate buffer instead of conventional phosphate buffer for enhanced detection.
- Employed isoelectric focusing on a pH 3-10 Ampholine gradient for protein separation.
- Applied differential elution from a DEAE-Sepharose column for complete enzyme separation.
Main Results:
- Detected two distinct kynurenine aminotransferases (KATs), designated KAT I and KAT II.
- KAT I prefers pyruvate as a cofactor with a pH optimum of 9.6.
- KAT II shows equal activity with pyruvate or 2-oxoglutarate and has a pH optimum of 7.4.
- KAT I and KAT II exhibit different sensitivities to amino acids and kinetic properties.
Conclusions:
- The human brain possesses at least two distinct KAT enzymes involved in KYNA production.
- These enzymes exhibit unique biochemical properties, suggesting differential roles in regulating cerebral KYNA synthesis.
- Further research is needed to elucidate the specific contribution of each enzyme to KYNA levels and its modulation of excitatory amino acid receptors.