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We have developed a method for the isolation of transport mutants with increases in velocity of transport through the A and ASC systems and through a newly discovered P system utilizing the amino acid antagonism between A system amino acids and proline in CHO-K1 pro- cells. Mutants alar2 and alar3, isolated in a single-step procedure, resistant to 25 mM alanine in MEM-10 plus 0.05 mM proline are pro-, stable, cross resistant to alpha-(methylamino)isobutyric acid (MeAIB) and show an approximately twofold increase in the initial velocity of proline uptake. Ethyl methane sulfonate (EMS) increases the frequency of pro- alar clones in the population by at least 50 times the spontaneous frequency. The increased velocity of proline transport by alar2 and alar3 can be attributable to the 1.5 to 3 times increase in velocity of transport of proline through systems A, ASC, and P. The Vmax for proline transport through the A system has increased two times for alar2 while the Km and Vmax for alar3 has increased by 1.4 and 2.3 times that of CHO-K1. There is a corresponding increase in Vmax of proline transport by alar2 through the P system. The P system is defined operationally as that portion of the Na+-dependent velocity that remains when the A, ASC, and glutamine-inhibitable fraction are eliminated. The system is concentrative. Proline appears to be the preferred substrate. Li+ cannot be substituted for Na+. The system is moderately dependent upon pH. It obeys Michaelis-Menten kinetics and is not derepressible by starvation. There is no evidence for an N system in CHO-K1.
J Moffett, and
S Curriden, and
R Ertsey, and
E Mendiaz, and
E Englesberg
October 1981,
The Journal of biological chemistry,
J Moffett, and
S Curriden, and
R Ertsey, and
E Mendiaz, and
E Englesberg
March 1984,
Somatic cell and molecular genetics,
J Moffett, and
S Curriden, and
R Ertsey, and
E Mendiaz, and
E Englesberg
January 1978,
Mutation research,
J Moffett, and
S Curriden, and
R Ertsey, and
E Mendiaz, and
E Englesberg
February 1994,
Proceedings of the National Academy of Sciences of the United States of America,
J Moffett, and
S Curriden, and
R Ertsey, and
E Mendiaz, and
E Englesberg
May 1987,
Biochemistry,
J Moffett, and
S Curriden, and
R Ertsey, and
E Mendiaz, and
E Englesberg
December 1988,
Infection and immunity,
J Moffett, and
S Curriden, and
R Ertsey, and
E Mendiaz, and
E Englesberg
December 1997,
DNA and cell biology,
J Moffett, and
S Curriden, and
R Ertsey, and
E Mendiaz, and
E Englesberg
March 1996,
Somatic cell and molecular genetics,
J Moffett, and
S Curriden, and
R Ertsey, and
E Mendiaz, and
E Englesberg
February 1981,
Journal of cellular physiology,
J Moffett, and
S Curriden, and
R Ertsey, and
E Mendiaz, and
E Englesberg
January 2004,
Methods in molecular biology (Clifton, N.J.),
