The tissue distribution, the subcellular distribution in liver, and the developmental patterns of cysteine:α-ketoglutarate aminotransferase (CAT) and 3-mercaptopyruvate sulfurtransferase (MPST) activities were determined in rats of the Sprague-Dawley strain. CAT activity was highest in heart and liver, whereas MPST activity was highest in liver and kidney. CAT activity was located primarily in the mitochondrial fraction with a low level of activity in all other fractions. MPST activity was located in both the mitochondrial and cytosolic fractions. The specific activity of CAT and MPST generally increased in rat liver, heart, and kidney during the developmental period from 18 days of gestation to 26 days after birth. Peak CAT-specific activity occurred at about 4 days of age and peak MPST activity occurred at about 21 days of age; peak activity of both CAT and MPST exceeded the adult specific activities. The distribution and developmental pattern of hydrogen sulfide production from cysteine, catalyzed by the coupled activities of CAT and MPST, was similar to those of CAT activity.

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