External irradiation of the hypophysis for Cushing's disease

During the past 12 years 17 patients with Cushing''s disease (bilateral adrenal hyperplasia secondary to excessive pituitary adrenocorticotrophic hormone) have been treated initially with external pituitary irradiation. Of the 15 patients who have had adequate follow-up, nine showed complete biochemical remission, and one showed biochemical improvement. There were no complications. It is therefore recommended that the first mode of therapy for all patients with Cushing''s disease should be pituitary irradiation if the patient''s clinical condition permits.     

PUBLIC HEALTH REPORT: Increase in Arthropod-Borne Encephalitis a Possibility

THE COMMUNICATION below is the first of what is intended as a continuing series of reports from the State of California Department of Public Health on topics of interest to physicians in private practice. On a number of occasions in the past, Dr. Malcolm H. Merrill, Director of Public Health, has appeared before the Council of the California Medical Association with intensely interesting reports on matters of public health and the attitudes and functions of the department. Since the minutes of the meetings of the Council give only the briefest of notes on such communications, Dr. Merrill was asked—and has agreed—to make use of this section of California Medicine for public health reports that can be informative and useful to all members.     

THE EFFECT OF ENZYME PURITY ON THE KINETICS OF TRYPTIC HYDROLYSIS

The rates of digestion of keratose have been determined with three commercial enzymes, ranging widely in strength. It has been found that the weaker the enzyme preparation, the more nearly does the course of the hydrolysis conform to that of a reaction of the first order. This has been explained on the assumption that in solution an equilibrium exists between active enzyme, and enzyme combined with inert material. In very impure enzyme preparations, the large quantities of combined enzyme act as a reservoir for active enzyme, maintaining a constant concentration of active enzyme during the course of the digestion.     

A fluorescence investigation of the active site of Pseudomonas aeruginosa exotoxin A.

Single tryptophan mutant proteins of a catalytically active domain III recombinant protein (PE24) from Pseudomonas aeruginosa exotoxin A were prepared by site-directed mutagenesis. The binding of the dinucleotide substrate, NAD+, to the PE24 active site was studied by exploiting intrinsic tryptophan fluorescence for the wild-type, single Trp, and tryptophan-deficient mutant proteins. Various approaches were used to study the substrate binding process, including dynamic quenching, CD spectroscopy, steady-state fluorescence emission analysis, NAD+-glycohydrolase activity, NAD+ binding analysis, protein denaturation experiments, fluorescence lifetime analysis, steady-state anisotropy measurement, stopped flow fluorescence spectroscopy, and quantum yield determination. It was found that the conservative replacement of tryptophan residues with phenylalanine had little or no effect on the folded stability and enzyme activity of the PE24 protein. Dynamic quenching experiments indicated that when bound to the active site of the enzyme, the NAD+ substrate protected Trp-558 from solvent to a large extent but had no effect on the degree of solvent exposure for tryptophans 417 and 466. Also, upon substrate binding, the anisotropy of the Trp-417(W466F/W558F) protein showed the largest increase, followed by Trp-466(W417F/W558F), and there was no effect on Trp-558(W417F/W466F). Furthermore, the intrinsic tryptophan fluorescence exhibited the highest degree of substrate-induced quenching for the wild-type protein, followed in decreasing order by Trp-417(W466F/W558F), Trp-558(W417F/W466F), and Trp-466(W417F/W558F). These data provide evidence for a structural rearrangement in the enzyme domain near Trp-417 invoked by the binding of the NAD+ substrate.     

The reactions of the phosphorylated pathway of L-serine biosynthesis: thermodynamic relationships in rabbit liver in vivo

The thermodynamic relationships among the reactions of the phosphorylated pathway of L-serine biosynthesis have been determined in rabbit liver in vivo in different dietary states. The mass action ratios of the reactions involved were calculated from the concentrations of appropriate metabolites in freeze-clamped liver and compared with the equilibrium constants of the same reactions previously determined under physiological conditions. Toward this goal, a new, highly specific enzymatic assay for L-phosphoserine was developed to allow the accurate measurement of this intermediate in biological material. The level of L-phosphoserine, the immediate precursor of L-serine, varied significantly with diet, being 0.81, 0.38, and 0.21 mumol/g wet wt in the fed, and 24 h and 48 h fasted states, respectively. The tissue content of L-phosphoserine was also sensitive to anoxia, falling almost fivefold within 5 min after the liver was removed. Values of for the combined reactions of the first two steps of the pathway of L-serine biosynthesis [D-3-phosphoglycerate dehydrogenase (EC 1.1.1.95) and L-phosphoserine aminotransferase (EC 2.6.1.52)] in livers from animals in different dietary states were calculated to be 1.2 X 10(-4) (fed), 1.4 X 10(-4) (24 h starved), and 0.70 X 10(-4) (48 h starved), all being very close to the value of the combined equilibrium constant of the same reactions (2.44 X 10(-4). Even when there were major changes in the individual components of, such as a fivefold drop in L-phosphoserine and a sevenfold fall in alpha-ketoglutarate following 5 min of anoxia, remained relatively unchanged (2.7 X 10(-4). Thus, it has been concluded that, in rabbit liver under most normal conditions, the combined reactions of D-3-phosphoglycerate dehydrogenase and L-phosphoserine aminotransferase remain very near equilibrium, and that almost all of the disequilibrium of the pathway, amounting to a delta G of -5.5 kcal/mol in the fed state, is at the last step, the L-phosphoserine phosphatase reaction (EC 3.1.3.3).