Comparison of the asymmetry of the hexose transfer system in the red cell of the newborn guinea-pig and human by permeability studies

Abstract

A comparison has been made between the hexose transferring system of erythrocytes from fetal and newborn guinea-pig cells and that of the human erythrocyte.

The kinetic parameters of 3-0-methyl glucose exchange in fetal and newborn guinea-pig cells have a higher constant for maximal exchange but show a lower affinity than in human erythrocytes.

Both systems show asymmetry of affinities toward nontransportable inhibitors such as 4-6-0-ethylidene-alpha-D-glucopyranose (ethylidene glucose) and methyl-2,3-di-0 methyl-alpha-D-glucopyranoside (trimethyl glucoside) but that in newborn guinea-pig cells is less than that in human erythrocytes.

Cytochalasin B competitively inhibits hexose exchange in newborn guinea-pig cells as it does in human cells but the K_i value was larger suggesting a lower affinity Exits were inhibited in an apparently non-competitive manner as occurs in human cells.

Cytochalasin B binding was studied and indicated that there were fewer hexose transferring components in newborn guinea-pig cells but as the maximal value for exchange is greater it may be presumed that the turnover number must be larger.

The inhibition of the two systems by the biphenolic inhibitors phlorizin, phloretin and polyphloretin phosphate was similar but there were differences in the K_i values.

The sensitivity to the irreversible inhibitors fluoro-dinitrobenzene and bromo-dinitrobenzene were also similar but there were differences in the effects of incubation in the presence of the transportable sugar 2-deoxyglucose.

It is concluded that the hexose transferring system in the two species is very closely related and that the differences are not more than might be expected in functional proteins taken from divergent species.