Partial characterization and purification of the glycosylation site recognition component of oligosaccharyltransferase

Oligosaccharyltransferase, the enzyme catalyzing the co-translational transfer of oligosaccharide from dolichyl-PP-GlcNAc2Man9Glc3 to -Asn-X-Ser/Thr- sequences in nascent polypeptide chains, was studied in hen oviduct microsomes using the active site-directed photoaffinity probe 125I-labeled N alpha-3-(4-hydroxyphenylpropionyl)-Asn-Lys(N epsilon-p-azidobenzoyl)-Thr-NH2. Several lines of evidence established that the tripeptide probe interacted with a 57-kDa protein of the endoplasmic reticulum that was subsequently glycosylated and converted to a 60-kDa form. The 57-kDa protein, isolated by two-dimensional gel electrophoresis, was used as immunogen to prepare polyclonal antisera. The specificity of the antibody was established on the basis of its ability to 1) recognize the 57-kDa protein by immunoblotting and 2) immunoprecipitate the photolabeled protein. The antibody also recognized photolabeled protein from different tissues and organisms. The 57-kDa protein isolated by immunoprecipitation retained its ability to interact with the photoaffinity probe but was inactive in catalyzing glycosylation of peptides. This result suggests that the 57-kDa protein is the component of oligosaccharyltransferase that recognizes the glycosylation site in polypeptides. These results are discussed in terms of possible models for the structure of oligosaccharyltransferase in the endoplasmic reticulum.     

The effect of vitamin B6 supplements on development of seizures in the gerbil, Meriones unguiculatus.

To see if a Vitamin B6 deficiency is responsible for seizure-proneness in the gerbil, $\text{Meriones unguiculatus}$, a diet supplemented with 0.5mg of pyridoxine per gram of Purina Lab Chow was fed to 8 experimental (E) mated pairs and their litters while 8 control (C) pairs and their litters were fed Purina Lab Chow which contains .004mg per gram of pyridoxine. All litters were tested for seizures every 2 weeks from 2 through 7 mos. of age once a month in a standard (SS) test cage and 2 weeks later in a clean home cage (CC) — and again at 1 yr in the SS cage. There were no differences on any of the measures between E and C litters. Significantly more seizures were elicited in the SS than in the CC tests, and the SS test became increasingly more effective with age. It was concluded that gerbil seizures were not due to a Vitamin B6 deficiency and that some age-related process might be a productive area for future investigation.     

The surgical treatment of necrobiosis lipoidica diabeticorum.

We review the literature on the surgical treatment of necrobiosis lipoidica diabeticorum, and we describe 7 cases treated at Stanford University Medical Center. Experiences with them prompt us to recommend surgical excision of the lesions down to the deep fascia, ligation of the associated perforating blood vessels, and the use of split-skin grafts to cover the defects. There were no recurrences when we did all these things.     

Activation of teratocarcinoma-derived hemoglobin genes in teratocarcinoma-Friend cell hybrids.

Hybrid cells formed by the fusion of murine teratocarcinoma and Friend erythroleukemia cells synthesize hemoglobin in the presence of chemical inducers such as dimethylsulfoxide (DMSO). By making use of the fact that the parental teratocarcinoma and Friend cells carried different alleles at the locus coding for the alpha chain of hemoglobin, it was possible to demonstrate that the teratocarcinoma-derived genes for the globin alpha chains are genetically active in hemoglobin-synthesizing hybrid cells. In addition, evidence is presented suggesting that the teratocarcinoma-derived genes for the beta-globin chains may also be expressed in the hybrids. Apparently the teratocarcinoma-derived genome has become reprogrammed to express erythroid functions following fusion of the teratocarcinoma cell to the Friend cell.     

Energization and activation of inorganic carbon uptake by light in cyanobacteria

The requirement of the inorganic carbon (C_i) transport system for light in cyanobacteria was investigated in Anabaena variabilis by the filtering centrifugation technique and in a mutant (E₁) isolated from Anacystis nidulans using a gas exchange system. C_i transport capability increased with time of preillumination and decreased following darkening. Full activity could not be obtained by operating either photosystem II (PSII) or photosystem I alone. 3(3,4 Dichlorophenyl)-1,1 dimethylurea strongly inhibited C_i uptake. Very low activity of PSII was sufficient to activate C_i uptake. However, in the presence of dithiothreitol PSII activity was not required. We conclude that light may be required to activate as well as to energize C_i uptake in cyanobacteria.     

Rhythmic activity of the endbrain in the carp evoked by adequate visual stimulation

In acute experiments on immobilized carps, under dark adaptation conditions, studies have been made on the electrical activity of the telencephalon and midbrain tectum. It was found that in the latter photostimulation evokes local rhythmic activity which includes fast (30-50 Hz) phasic (200-300 ms) and slow (8-14 Hz) tonic (up to 3-4 s) components. High rhythm of this activity may be observed only in "healthy" preparations, coinciding with on-rhythm in the midbrain tectum. Low rhythm does not depend on the presence of rhythmic activity in the tectum. Various aspects of the development of the thalamo-telencephalic system in vertebrates are discussed.     

Reference ranges of retinol, tocopherols, lycopene and alpha- and beta-carotene in plasma by simultaneous high-performance liquid chromatographic analysis

Using a high-performance liquid chromatographic procedure, age- and gender-based reference ranges for plasma retinol, alpha- and gamma-tocopherol, lycopene, and alpha- and beta-carotene have been established. In addition to confirming higher retinol levels in men than in women (p less than 0.001), this study demonstrates significantly higher plasma levels of both carotenes in women than in men (p less than 0.001). The plasma levels of retinol and beta-carotene showed a positive relationship with age after adjusting for plasma lipids (p less than 0.001 and p less than 0.02, respectively). In contrast to beta-carotene, there was no gender difference for plasma lycopene and a strong (p less than 0.001) inverse relationship of lycopene with age. These results suggest that differences may exist between beta-carotene and lycopene in their intestinal absorption, plasma transport, or tissue metabolism.