Comparison of phosphofructokinases in submandibular glands of immature and adult rats.

1. Phosphofructokinases (PFKs) in immature and adult rat submandibular glands were purified to near homogeneity, and their properties were compared. 2. PFK in immature gland was less sensitive to inhibition by ATP than adult PFK. 3. Saturation curve for fructose 6-phosphate of PFK in immature gland was less sigmoidal than that of adult PFK indicating the lower cooperativity of subunits in immature PFK. 4. Fructose 2,6-bisphosphate relieved PFK from inhibition by ATP in adult gland, but a similar effect was not clearly observed in immature gland PFK. 5. Adult PFK was a heterotetramer consisting of C-, M-, L-subunits, but in immature PFK another type of subunit, which was slightly smaller than L-subunit, existed in addition to C-, M- and L-subunits.