Cystathionase Deficiency: the Effect of Cofactor on the Stability of Normal and Abnormal Enzyme from Lymphoid Cell Lines

Abstract

Heating at 70 °C with and without added pyridoxal phosphate (PLP) had strikingly different effects on cystathionase protein from normal long-term lymphoid cell lines and on the enzyme from cells derived from patients with vitamin-B6-responsive cystathioninuria. PLP added to extracts of normal cells afforded complete protection against heat inactivation, whereas inactivation of the cystathionase protein in extracts obtained from two cystathioninuric lines was greater in the presence of PLP than in its absence.

Vitamin B-6 and Sulfur Amino Acid Metabolism

“…This mutant enzyme retains antigenic identity with the normal enzyme, although the antigenic binding capacity may be reduced. Another interesting demonstration of an altered structure of the mutant enzyme resulted from the measurement of the thermostability of the enzymatic activity, and the effect of pyridoxal 5'-phosphate on this parameter (83). Extracts of cells from normal individuals were inactivated to varying degrees by heating at 70 0 for 90 minutes prior to measurement of cystathionase activity.…”