Antonio H. Romano

Properties of the hexose transport systems of Aspergillus nidulans

Abstract 1. 1. Systems for the transport of d -glucose, d -galactose, and d -fructose by young mycelium of Aspergillus nidulans were studied. Properties of the glucose system were determined by use of isotopic 2-deoxy- d -glucose, a nonutilizable glucose analog; the uptake of isotopic d -galactose and d -fructose were measured by mutants that could not metabolize these sugars. 2. 2. Systems for the transport of these three sugars, are constitutive and carrier-mediated, since they show saturation kinetics with respect to concentration, and are subject to competitive inhibition. 3. 3. The uptake of all three sugars takes place against a concentration gradient, and is energy dependent. 4. 4. The relationship between structure and affinity for the transport systems was studied by measurement of competitive inhibition exerted by various sugars and their derivatives on the uptake of 2-deoxy- d -[14C6]glucose and d -[14C6]galactose. Sugars could thus be ordered with respect to their affinities for the transport systems. 5. 5. In the case of both the d -glucose and d -galactose systems, no single substituent of the C1 pyranose ring was essential for carrier-binding activity; any single change was tolerated, with the exception of methylation of the anomeric hydroxyl group. Any two changes abolished activity. 6. 6. While d -galactose competes for the d -glucose system and vice versa, systems for the transport of these two sugars are distinct. 7. 7. d -Fructose is transported by a highly specific system, since no sugar tested competed with its uptake.

Pyruvate carboxylase of Rhizopus nigricans and its role in fumaric acid production

Abstract The chief carbon dioxide-fixing system in a fumaric acid-producing strain of Rhizopus nigricans is an acetyl coenzyme A - dependent pyruvate carboxylase. This enzyme is produced in high levels during the period of rapid glucose utilization, and precedes fumarate accumulation. It is proposed that this system is the principal anaplerotic CO2 fixing mechanism in this organism, and its continued operation in high glucose media after biosynthesis has ceased results in production of fumaric acid.

Zinc Stimulation of RNA and Protein Synthesis in Rhizopus nigricans

Addition of 1.7 x 10-5M zinc sulfate to cultures of Rhizopus nigricans increases growth and substrate utilization. Analysis of cells during the course of growth, after addition of the metal, showed that there was an immediate increase in RNA, followed by a corresponding increase in protein and cell mass. The DNA content was affected to a lesser extent. It is postulated that Zn++ stimulates growth through a primary effect on RNA synthesis.

Sugar uptake by germinating Bacillus subtilis spores

The phosphoenolpyruvate (PEP) phosphotransferase system first described by Kundig, Ghosh and Roseman 1 l] , which has been shown to play an important role in the transport of sugars by a number of bacteria [2] , has been detected in a number of species of Bacillus [3,4] . This investigation was carried out to determine whether this system was present in dormant spores, or whether it was synthesized during or following the germination process, and to determine the temporal relationship between germination and the functioning of an active glucose transport system. It was found that the complete transport system was present in dormant spores of Bacillus sub tilis, and that spores began actively to transport the non-metabolizable glucose analog 2-deoxy-D-glucose a short time after the commencement of germination.