Search

To gain insight into the uptake of mature aspartate aminotransferase by isolated mitochondria, the capability of certain cyanogen bromide peptides from mature beef heart mitochondrial aspartate aminotransferase to inhibit enzyme uptake was kinetically tested. N-terminal peptides (1-9 and 10-31) proved to inhibit the rate of aspartate aminotransferase uptake respectively in purely competitive and non-competitive ways, whereas other peptides distal from the N-terminus (203-217, 321-327 and 328-353) were found to be completely ineffective.

Fumarate permeation in isolated rat liver mitochondria was demonstrated by measuring malate and phosphate efflux caused by fumarate added externally to the mitochondrial suspension. The existence of two specific fumarate translocators, fumarate/malate and fumarate/phosphate, is shown here. These carriers are distinguished in the light of different kinetic parameters (Km values are 50 microM and 150 microM, and Vmax values are 17 and 40 nmoles/min X mg mitochondrial protein, respectively) and of differing sensitivity to non-penetrant compounds. Fumarate was found to cause oxaloacetate efflux from mitochondria by means of an indirect process which involves the cooperation of both fumarate/malate and malate/oxaloacetate translocators. Results are discussed in the light of the physiological role played by fumarate translocation in both ureogenesis and aminoacid metabolism.