The biosynthesis of hydroxynalidixic acid.

Analytical methods have been worked out for the study of the human metabolism of nalidixic acid. Under pathological conditions the excretion of its metabolites differed from that observed in healthy volunteers. The cause of these variations was studied on the basis of individual excretion curves. The results showed that human and microbial biotransformations were identical. The possibilites offered by the new methods in drug research are discussed.     

The precipitation of poly-L-glutamic acid. II. beta-Precipitation.

Infrared and X-ray diffraction studies have established that in the β-precipitation region of poly-L -glutamic acid the chains are in the β-conformation. Therefore, a major molecular conformational change has taken place upon precipitation. It is shown that the size of the α-helical aggregates remains constant with time in the β-region. Strong evidence can be offered to indicate that the transformation involves a transitory random-coil intermediate. Reasons are advanced, in view of the stability of the β-form, as to why two distinct precipitation regions exist.     

The precipitation of poly-L-glutamic acid. I. Alpha-precipitation.

Studies have been made of the precipitation of poly-L -glutamic acid from dilute aqueous solutions, over the pH range where the α-helical conformation is maintained. The major purpose is to establish the molecular conformation in the precipitate and to outline the mechanism of the precipitation. Utilizing molecular-weight fractions, it is shown that there are two distinctly different precipitation regions, which depend on temperature, concentration, and pH. In one of these regions, the α-region, a variety of physical properties demonstrate that precipitation occurs without any conformational change. The temperature coefficient of the precipitation process in this region indicates that it is nucleation-controlled.     

The hydrolytic activity of L-ascorbic acid.

The ability of L-ascorbic acid to catalyze the liberation of 4-methylumbelliferone from 4-methylumbelliferyl-beta-D-N-acetylglucosaminide, 4-methylumbelliferyl-beta-D-glucuronide, 4-methylumbelliferyl-alpha-D-mannoside, and 4-methylumbelliferyl-beta-D-galactoside is documented. There is an apparent metal and oxygen dependency. The cleavage of two lipids was shown in addition to the hydrolysis of these fluorogenic glycosides. Galactose was liberated from galactosyl-6-[3H]ceramide and oleic acid from cholesterol-[1-14C]oleate by L-ascorbic acid under conditins usually used for in vitro incubations. In common with most in vitro systems, only a small percentage of substrate was degraded.