PROTEINS AS BUFFERS

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75001/1/j.1749-6632.1966.tb50706.x.pd

Precautions that we are observing one transport system unobscured by the contributions of others

No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49871/1/1040890416_ftp.pd

TRANSPORT OF AMINO ACIDS

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75151/1/j.1753-4887.1963.tb04736.x.pd

Amino acid transport systems in animal cells: Interrelations and energization

After summarizing the discrimination of the several transport systems of neutral amino acids in the cell of the higher animal, I discuss here the ways in which 2 dissimilar transport systems interact, so that one tends to run forward for net entry and the other backwards for net exodus. An evaluation of the proposals for energization shows that uphill transport continues when neither alkali-ion gradients nor ATP levels are favorable. Evidence is presented that under these conditions a major contribution is made by another mode of energization, which may depend on the fueling of an oxidoreductase in the plasma membrane. This fueling may involve the export by the mitochondrion of the reducing equivalents of NADH by one of the known shuttles, e.g., the malate-aspartate shuttle. After depletion of the energy reseves in the Ehrilich cell by treating it with dinitrophenol plus iodoacetate concentrative uptake of test amino acids is restoration by pyruvate but in poor correlation with the restoration of alkali-ion gradients and ATP levels. This restoration by pyruvate but not by glucose is highly senstitive to rotenone. A combination of phenazine methosulfate and ascorbate will also produce transport restoration, before either the alkali-ion gradients or ATP levels have begun to rise. The restoration of transport applies to a model amino acid entering by the Na + -independent system, as well as to one entering by the principal Na + -dependent system, restoration being blocked by ouabain, despite the weak effect of ouabain on the alkali-ion gradients in the Ehrlich cell. Quinacrine terminates very quickly the uptake of model amino acids, before the alkali-ion gradients have begun to fall and before the ATP level has been halved. Quinacrine is also effective in blocking restoration of uphill transport by either pyruvate or the phenazine reagent. Preliminary results show that vesicles prepared from the plasma membrane of the Ehrlich cell quickly reduce cytochrome c or ferricyanide in the presence of NADH, and that the distribution of a test amino acid between the vesicle and its environment is influenced by NADH, quinacrine, and an uncoupling agent in ways consistent with the above proposal, assuming that a majority of the vesicles are everted.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38203/1/400060206_ftp.pd

Organic ion transport during seven decades the amino acids

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24700/1/0000119.pd

Efflux used as a fad word?

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24014/1/0000263.pd

Anions versus cations?

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32501/1/0000588.pd

Use of a mechanical model to convey the idea of energetic coupling

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23009/1/0000577.pd

Amino acid stimulation of alkali-metal-independent ATP cleavage by an Ehrlich cell membrane preparation

A stimulation by certain amino acids of the hydrolysis of ATP by a vesicular preparation from the Ehrlich ascites tumor cell has been observed, independently of the presence or absence of Na+, K+ or ouabain. This membrane preparation failed to show evidence for the presence of a characteristic amino-acid-stimulated, Na+--K+-dependent ATPase previously observed for other preprations. Stimulating activity is shown by two groups of abnormal substrates of Na+-independent transport System L, which elicit a structure-dependent energization of that system. For some of these amino acids, adding an ionophore served to bring out the stimulation of ATP cleavage.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33803/1/0000058.pd