Structure of maltoheptaose by difference Fourier methods and a model for glycogen

The structure of the glucose heptamer, maltoheptaose, has been determined by difference Fourier analysis at 0.25 nm resolution through its binding to phosphorylase a. It is a left-handed helical structure, with 6.5 glucose residues per turn and a rise per residue of 2.4 Å. The molecule shows short-range order when no protein is present to stabilize its conformation in solution. With one exception, the individual torsion angles between sugar residues vary over a narrow range and preserve a good O₍₂₎O_(3′) hydrogen bond. The length of an individual chain for glycogen can be extrapolated from the maltoheptaose data and agrees well with the size for glycogen predicted by the Whelan model.     

Plasma prolactin concentrations in breeding pied flycatchers (Ficedula hypoleuca) with an experimentally prolonged brooding period

This experiment explored the stimulatory effect of brooding newly hatched young on plasma prolactin concentration in male and female pied flycatchers, Ficedula hypoleuca. By exchanging offspring between nestboxes, one group of parents was exposed to 1- to 3-day-old nestlings for 12 days. Females in this group continued night-time brooding during these 12 days. The females, but not the males (who do not participate in brooding nestlings), after 6 days had higher plasma prolactin concentrations than control birds which had shown a 50% reduction in night-time brooding at this stage. By Day 12, however, prolactin concentration had decreased to the same level as in control birds, even though these females were still brooding 3-day-old nestlings. Female flycatchers given 3-day-old nestlings on the day their own eggs hatched showed an earlier reduction in night-time brooding and an earlier decrease in plasma prolactin than did control birds. An early decrease in prolactin was also seen in the males of this experimental group.     

The three-dimensional structure of acarbose bound to glycogen phosphorylase

Acarbose, a pseudotetrasaccharide with a conduritol ring at the nonreducing terminus, is a naturally occurring inhibitor of amylases. It is shown here to be an inhibitor of glycogen phosphorylase and to bind more tightly to the enzyme than the equivalent malto-oligosaccharide substrate. X-ray crystallographic studies of the acarbose-phosphorylase a complex in the presence of glucose and caffeine reveal the structure of acarbose as bound to the storage site of phosphorylase. The acarbose binds in an orientation such that the conduritol ring makes no protein contacts. As with malto-oligosaccharides bound at this site, the observed conformation of acarbose is stabilized by O-2-O-3' hydrogen bonding and is similar to, but not identical with, that predicted by hard-sphere exo-anomeric effect calculations and justified by 1H nuclear magnetic resonance studies (Bock, K., and Pedersen, H. (1984) Carbohydr. Res. 132, 142-149). Intramolecular O2-O3' hydrogen bonds appear to play an important role in stabilizing the conformation observed in these studies, even for those residues closely associated with the protein.     

Tyrosine aminotransferase deficiency in mink (Mustela vision): A model for human tyrosinemia II

Mink pseudodistemper, a recessive disease associated with high blood tyrosinelevels, is an animal analogue of the human inborn error of metabolism, tyrosinemia II. Affected mink and man have eye and skin lesions. Affected mink have no hepatic tyrosine aminotransferase (TAT) activity, as measured immunologically and biochemically. Hepatic mitochondrial aspartate aminotransferase is increased to 188% of control. This new genetic animal model of TAT deficiency should allow new studies of tyrosine metabolism.Supported by NIH Grants AM-17253 (LAG), 5T32-AM-07093 (LAG), and RCDA AM-0008 (LAG), grants from the Wisconsin State Mink Advisory Board, and a BRSG grant for the Graduate School of the University of Wisconsin, Madison, Publication No. 82 of the dermatology research laboratories of Duke University Medical Center.     

Thin-layer chromatographic collector-eluter.

A combination thin-layer chromatographic collector and elution apparatus is described. The device is designed to minimize manipulations and maximize accuracy and can be used for both analytical and small-scale preparative separations.     

Career choices of physicians 15 years after entering medical school.

The career status of 149 graduates of the University of Toronto faculty of medicine who entered in 1958 and graduated in 1962 was determined in 1973. The response rate to the mailed questionnaire was 96.6%. Of the graduates 4.7% were not practising medicine, 2.0% stated that medicine was not their primary gainful activity and 4.1% were untraceable or unknown. Of the 24 women in the class 17 (70.8%) were practising at least 76% of their time and 4 (16.7%) were practising 26 to 75% of their time. General practice or family medicine had been chosen by 39.0% of the class and a specialty by 55.7%; 5.4% were unknown or untraceable. The place of longest residence before entrance to university was a good predictor of ultimate location of practice but not of type of practice.