THREONINE-SENSITIVE HOMOSERINE DEHYDROGENASE AND ASPARTOKINASE ACTIVITIES OF ESCHERICHIA COLI K12 - BINDING OF THREONINE AND OF PYRIDINE NUCLEOTIDES - STOICHIOMETRY AND OPTICAL EFFECTS

The aspartokinase I‐homoserine dehydrogenase I of Escherichia coli K 12, composed of six subunits of molecular weight 60,000, binds cooperatively six molecules of l‐threonine. A maximum of three molecules of NADP+ or NADPH, measured by a number of techniques, is bound in the presence or in the absence of threonine. Characteristic effects of l‐threonine on the protein include a perturbation of its absorption and fluorescence spectra and a quenching of the fluorescence of the protein‐NADPH complex. These findings are discussed in view of the structure of the protein. Copyright © 1969, Wiley Blackwell. All rights reserved