Glucose induces two amino acid transport systems in Chlorella.

Abstract

In autotrophically grown ChloreUa.cells, glucose induces a hexose transport system but, at the same time, the synthesis of two amino acid transport systems is also induced. Thus, the rates of uptake of glycine, L-alanine, L-proline, and L-serine, all of which compete with each other for entry into the cells, increase more than 1004fold when the algae are pretreated with glucose. The rates of L-arginine and L-lysine uptake increase by a factor of 25 to 50. The accumulation of proline and arginine within the cells amounts to 200-and 600-fold, respectively. Glucose does not cause the positive effect on. amino acid uptake by serving as metabolic substrate because the nonmetabolizable 6-deoxyglucose also acts as inducer. Cycloheximide prevents the induction. The induced transport system for the four neutral amino acids has a turnover with a half-life of 7 hr, which corresponds closely to the half-life of the hexose transport system. The transport system for the basic amino acids, on the other hand, disappears with a half-life of 25 hr.Since the classical work of Rickenberg et al. (1) on the induction of the lac. permease in Escherichia coli, many inducible transport systems have been described for bacteria (2-4). In a few cases this phenomenon has also been observed for eukaryotic cells (5, 6). Wherever induction has been found, however, the inducing substrates were either transport substrates and analogues ofthese or, like allo-lactose (7), a physiological substance closely related to the transport substrate.It has been surprising, therefore, to find that glucose and nonmetabolizable glucose analogues act as inducers for two specific amino acid uptake systems in the unicellular alga Chlorella vulgaris. This autotrophically growing alga rapidly takes up various hexoses once a specific hexose transport system is induced by monosaccharides (6, 8). This transport ofhexoses is an active one and proceeds as proton symport (9, 10). This paper reports that Chlorella induced for sugar transport also shows an uptake rate for basic and neutral amino acids that is increased more than 100-fold compared to cells not pretreated with hexoses. MATERIALS AND METHODSThe strain of C. vulgaris and the growth conditions were as described (8).]alanine, and L-['4C]proline were obtained from New England Nuclear; all other radioactive L amino acids were a gift of A. Bock. 6-Deoxyglucose was tritiated by Amersham. Cycloheximide and the nonradioactive amino acids were obtained from Serva (Heidelberg, Federal Republic of Germany), and 6-deoxyglucose was from Koch-Light (Colnbrook, England).Uptake ofAmino Acids. The screening for amino acid uptake that might be stimulated by glucose was performed with 0.1 mM labeled amino acid in an algal suspension of50 t1u ofpacked cells per ml in the presence or absence of 15 mM glucose. The disappearance of radioactivity from the medium was determined by centrifugation of the cells in intervals (2 or 5 min) and measurement of residual radioactivity in the medium. When the uptake of an amino acid was...

Extracellular deamination of l-amino acids by Chlamydomonas reinhardtii cells

“…In contrast, Chlamydomonas reinhardtii 6145c cells can deaminate twelve L-amino acids by means of a deaminase activity which required acetate for induction and never occurred in nitrogen-free cultures. In this connection, the ratio carbon/ nitrogen has been proposed as responsible for the induction of an amino acid permease in Chlorella (Cho et al 1981), and a" superderepression" of asparaginase activity has been found in Saccharomyees cerevisiae cells incubated with glucose (Pauling and Jones 1980). Deaminase activity induction depended on de-novo protein synthesis, since cychloheximide prevented cells from deaminating amino acids (Fig.…”

“…This takes place either by means of energy-dependent transport systems (Kirk and Kirk 1978a, b;Cho et al 1981;Cho and Komor 1983;Flynn and Syrett 1985;Sauer and Tanner 1985) or by deamination mechanisms occurring at the cell surface with the subsequent uptake and assimilation of the ammonium produced Cooksey 1979, 1981a, b).…”

Regulation of amino acid uptake in conifers by exogenous and endogenous nitrogen

“…It is possible that the regulatory signal may not be an N compound at all, but a compound derived from, for example, carbon metabolism. Indeed, both glucose and non-metabolizable glucose analogues have been reported to induce amino acid transporters in algae, illustrating the tight interdependence of carbon and nitrogen metabolism (Cho et al 1981). The ability to up-regulate amino acid uptake in response to N deficiency suggests that amino acid uptake plays a significant role in the N scavenging of the plant.…”

Effect of dietary carbohydrate on monosaccharide uptake by mouse small intestine in vitro.

“…The simplest explanation is that glucose acts directly on intestinal cells, inducing synthesis of transport protein. Transported but nonmetabolized glucose analogues fail to mimic glucose's ability to restore monosaccharide transport in fasted rats (Roy & Dubois, 1972;Debnam & Levin, 1976), but do induce glucose transport in the alga Chlorella (Cho, Sauer, Komor & Tanner, 1981).…”