Abstract
D-Amino acid aminotransferase, purified to homogeneity and crystallized from Bacillus sphaericus, has a molecular weight of about 60,000 and consists of two subunits identical in molecular weight (30,000). The enzyme exhibits absorption maxima at 280, 330, and 415 nm, which are independent of the pH (5.5 to 10.0), and contains 2 mol of pyridoxal 5'-phosphate per mol of enzyme. One of the pyridoxal-5'-P, absorbing at 415 nm, is bound in an aldimine linkage to the epsilon-amino group of a lysine residue of the protein, and is released by incubation with phenylhydrazine to yield the catalytically inactive form. The inactive form, which is reactivated by addition of pyridoxal 5'phosphate, still has a 330 nm peak and contains 1 mol of pyridoxal 5'-phosphate. Therefore, this form is regarded as a semiapoenzyme. The holoenzyme shows negative circular dichroic bands at 330 and 415 nm. D-Amino acid aminotransferase catalyzes alpha transamination of various D-amino acids and alpha-keto acids. D-Alanine, D-alpha-aminobutyrate and D-glutamate, and alpha-ketoglutarate, pyruvate, and alpha-ketobutyrate are the preferred amino donors and acceptors, respectively. The enzyme activity is significantly affected by both the carbonyl and sulfhydryl reagents. The Michaelis constants are as follows: D-alanine (1.3 and 4.2 mM with alpha-ketobutyrate and alpha-ketoglutarate, respictively), alpha-ketobutyrate (14 mM withD-alanine), alpha-ketoglutarate (3.4 mM with D-alanine), pyridoxal 5'-phosphate (2.3 muM) and pyridoxamine 5'-phosphate (25 muM).
Highlights
D-Amino acid aminotransf’erase, purif’ied to homogeneity and crystallized from Bacillus sphaericus, has a molecular weight of about 60,000 and consists of two subunits identical in molecular weight (X0,000)
The first evidence for the occurrence of D-amino acid specific aminotransf’erase was found by Thorne et al [1, 2] in the cell-free extract of Bacillus subtilis and Bacillus anthracis. They showed that the: enzyme of B. subtilis was activated a few-fold by pyridoxal-5’-P’
(3), Bacillus sphuericus [4], and Bacillus licheniformis [5], and recently has been f’ound in higher plants [6, 7] and mammalian liver [8]. n-Alanine aminotransferase was purified to near homogeneity from B. subtilis to elucidate the enzymologic and kinetic properties [9,10,11]
Summary
The inactive form, which is reactivated by addition of pyridoxal 5’-phosphate, still has a 330 nm peak and contains 1 mol of pyridoxal5’-phosphate. This form is regarded as a semiapoenzyme. The first evidence for the occurrence of D-amino acid specific aminotransf’erase was found by Thorne et al [1, 2] in the cell-free extract of Bacillus subtilis and Bacillus anthracis. They showed that the: enzyme of B. subtilis was activated a few-fold by pyridoxal-5’-P’. Of the crystalline n-amino acid aminotransferase are described with particular emphasis on the bound pyridoxal-j’-P
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