Properties of soluble and particulate cysteine sulfinate decarboxylase of the adult and the developing rat brain

Abstract

Some properties of cysteine sulfinate decarboxylase (CSD) activity were studied in the pellet and supernatant of a 18,000 X g centrifugation of isotonic sucrose rat brain homogenates. About 50% of the enzyme activity was found associated to the particulate fraction and 16% of the activity remained particle bound after hypo-osmotic shock of the 18,000 X g pellet. The activity of the 18,000 X g supernatant showed a lower dependence on exogenous pyridoxal phosphate (PLP) than the activity in the particulate fraction. The CSD activity of these fractions also differed in optimal pH and in apparent kinetic constants. The enzyme associated to particles showed the highest Vmax and the lowest Km. The activity and kinetic characteristics of CSD were studied during brain postnatal development. In the newborn brain only a small amount of the enzyme activity was found associated to the 18,000 X g pellet. CSD in brain homogenates of immature rats was less dependent on free PLP and showed a higher Km and a lower Vmax as compared with the enzyme in the adult brain. Between birth and adulthood the enzyme activity increased more than 10-fold in the particulate fraction and 2-fold in the soluble fraction. It is concluded that the differences observed in CSD activity between newborn and adult brain are due to an increase of the particulate form of the enzyme during postnatal development.