The thymic differentiation markers T6 and M241 are two unusual MHC class I antigens

The human beta 2-microglobulin (beta-2m)-associated human thymocyte differentiation antigens T6 and M241 were compared using biochemical techniques. T6 and M241 antigens reside on different molecules with apparent m.w. of 49,000 and 43,000, respectively. Here we show that both proteins have a protein backbone m.w. of 33,000. In addition, T6 and M241 have a large portion of their peptides in common. When we compared the protein backbone m.w. of T6 and M241 with the murine beta-2m-associated thymus leukemia (TL) antigens, we found a considerable difference in size, suggesting that T6 and M241 may not be human homologues of TL antigens and constitute a novel type of major histocompatibility (MHC) class I antigens.     

Spectroscopic studies on Neurospora copper metallothionein

The spectral properties of Neurospora copper metallothionein were investigated and compared with those of the Cu(I)-2-mercaptoethanesulfonic acid complex. In both cases, the absorption spectra are rather similar, showing a characteristic shoulder at approximately 250 nm. However, marked differences were observed in their emissive properties. Thus, only metallothionein emits detectable luminescence in solution, but both the copper protein and the Cu(I) complex are luminescent at 77 K. The circular dichroism spectrum of Neurospora copper metallothionein shows several Cotton extrema attributable to asymmetry in metal coordination. The influence of HgCl2 and p-(chloromercuri)benzoate on the spectral properties of metallothionein was also investigated. The two mercurials exerted a pronounced effect on the electronic absorption, chiroptical, and emissive properties of the protein. Spectroscopic titrations followed by gel filtration experiments indicate that two mercurials can be bound per metallothionein molecule without loss of copper. This binding is responsible for the disappearance of the emissive properties of metallothionein and for the distinct changes in its electronic absorption and circular dichroism spectra. From these data, it is suggested that the Cu(I) ions are coordinated to the cysteinyl residues in the form of a single metal cluster.     

Neurospora tyrosinase: structural,spectroscopic and catalytic properties

Summary Tyrosinase is a copper containing monooxygenase catalyzing the formation of melanin pigments and other polyphenolic compounds from various phenols. This review deals with the recent progress on the molecular structure of the enzyme from Neurospora crassa and the unique features of the binuclear active site copper complex involved in the activation of molecular oxygen and the binding of substrates. The results of the spectroscopic properties of Neurospora tyrosinase will also be discussed in the light of the structural similarity of the copper complex in the oxygen binding hemocyanins.     

Nucleotide pools of growing,synchronized and stressed cultures of Saccharomyces cerevisiae

High pressure liquid chromatography has been used to study the acid soluble nucleotide pool of Saccharomyces cerevisiae under different conditions of growth. ATP, ADP, AMP, NAD, GTP, UTP, UDP, CTP, CDP, and UDP-sugars plus UMP could be separated and were found in concentrations higher than 0.1 mumol per g yeast cell dry weight (= detection limit). During glucose-limited continuous culture the levels of individual nucleotides depended on the growth rate, which was most pronounced with pyrimidine (uridine, cytidine) nucleotides. The energy charge (E.C.) remained high (0.9) at all growth rates (0.07-0.3 h-1). During synchronized growth at a constant growth rate (0.11 h-1) almost all nucleotide levels and the E.C. remained at constant values with the only exception of UDP-sugars and UMP of which increased levels were found during the phase of budding. Under conditions of metabolic stress (addition of antimycin A, deoxyglucose plus iodoacetate) pronounced changes in the levels of purine (adenine and guanine) nucleotides and the E.C. were observed. All other nucleotides were less influenced by these conditions. Only under these conditions IMP accumulation was observed. The results strongly argue against the significance of purine nucleotide or E.C. measurements under viable conditions. In contrast, changes in the levels of pyrimidine nucleotides seem to be indicative of changes in the flux through the metabolic pathways where they act as coenzymes.     

Effects of potassium,lanthanum and black widow spider venom on miniature synaptic potentials in theTorpedo electroplax

Summary Using a method of focal drug application it is demonstrated that high potassium concentration, lanthanum, and black widow spider venom accelerate spontaneous transmitter release inTorpedo electric tissue.This investigation was supported by the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 138). Thanks are due to Dr. R. Martin and the staff of the Stazione Zoologica, Naples, for supplyingTorpedo, and Dr. N. Frontali, Rome, for a gift of frozen black widow spiders.     

The effect of energization on the apparent Michaelis–Menten constant for oxyge in nmitochondrial respiration

Lineweaver-Burk plots of 1/v against 1/[O(2)] for rat liver mitochondrial respiration with succinate or ascorbate+NNN'N'-tetramethyl-p-phenylenediamine as substrates are non-linear. In state 3u (uncoupled by trifluoromethoxycarbonyl cyanide phenylhydrazone) such plots tend to be concave upward, whereas in state 4 (energized) the plots were concave downward. The apparent K(m) for oxygen is larger in state 4 than in state 3u, despite the higher turnover in the latter system. It is postulated that at least one reversible reaction occurs between cytochrome c and cytochrome c oxidase, whose rate is increased on energization (reversed electron transfer); a model including such a reaction is proposed which accounts semiquantitatively for the observations.     

Effect of arterial perfusion on net water flux and active sodium transport across the isolated skin ofBufo bufo bufo (L.)

Summary A method has been developed which allows perfusion of the blood vessels in isolated pelvic skins ofB. bufo. The effect of various doses of vasotocin (AVT) on net water flux (inside medium 220 mOsM, outside medium 11 mOsM) and active sodium transport were compared in perfused and unperfused skins. The unstimulated water flux (Fig. 3) and the active sodium transport (Fig. 6) were unaffected by perfusion. The threshold for stimulation of water flux was between 0.01 and 0.1 nM vasotocin in perfused skins and between 0.1 and 1 nM in unperfused skins. The threshold for stimulation of active sodium transport was between 0.005 and 0.05 nM vasotocin in perfused skins and between 0.05 and 0.5 nM in unperfused skins. The maximal water flux through perfused skins, 4 l/cm²min, was obtained at 1 nM vasotocin. At 10 nM vasotocin the water flux was only 0.7 l/cm²min in unperfused skins. The maximal active sodium transport was approximately of the same magnitude in perfused and unperfused skins, at 0.5 mM and at 50 nM, respectively.