ISSN:
0148-7280
Keywords:
methionine uptake
;
methionine efflux
;
kinetic parameters
;
trans-stimulation
;
trans-inhibition
;
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
Notes:
The mouse egg is an ideal model for the kinetic study of neutral amino acid exchange transport in development in that it possesses strong exchange-mediated uptake/efflux with little other efflux. Exchange transport was examined by preloading eggs in unlabeled or labeled amino acid and then measuring subsequent amino acid fluxes. The existence of two L-like (leucine-preferring) systems, a low-affinity exchange system, and a high-affinity weakly exchanging system is suggested by the differences between preloaded and control eggs in uptake specificity and in the kinetic parameters of methionine uptake (respectively, Km = 220 and 69 μM, Vmax = 98 and 32 fmol/min/egg). The Vmax of exchange-mediated efflux of methionine is similar to that for uptake into preloaded eggs, but the Km is about an order of magnitude higher. Preloading in alanine and serine (preferred substrates, along with cysteine, of system ASC) decreased the subsequent uptake of radiolabeled methionine, suggesting some ASC activity in the unfertilized mouse egg. The plateau in accumulation of leucine and phenylalanine, characteristic of simple exchange (mediated by system L), is not shared by methionine, suggesting the existence of another system (possibly an A, or alanine-preferring, system) for the transport of methionine. Amino acid transport in the mouse egg is more complex than previously thought, the egg possessing four interacting systems for the transport of the neutral amino acids.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrd.1120150102
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