Henry B. Skinner

Phospholipid transfer activity is relevant to but not sufficient for the essential function of the yeast SEC14 gene product.

To investigate several key aspects of phosphatidylinositol transfer protein (PI‐TP) function in eukaryotic cells, rat PI‐TP was expressed in yeast strains carrying lesions in SEC14, the structural gene for yeast PI‐TP (SEC14p), whose activity is essential for Golgi secretory function in vivo. Rat PI‐TP expression effected a specific complementation of sec14ts growth and secretory defects. Complementation of sec14 mutations was not absolute as rat PI‐TP expression failed to rescue sec14 null mutations. This partial complementation of sec14 lesions by rat PI‐TP correlated with inability of the mammalian protein to stably associate with yeast Golgi membranes and was not a result of rat PI‐TP stabilizing the endogenous sec14ts gene product. These collective data demonstrate that while the in vitro PI‐TP activity of SEC14p clearly reflects some functional in vivo property of SEC14p, the PI‐TP activity is not the sole essential activity of SEC14p. Those data further identify an efficient Golgi targeting capability as a likely essential feature of SEC14p function in vivo. Finally, the data suggest that stable association of SEC14p with yeast Golgi membranes is not a simple function of its lipid‐binding properties, indicate that the amino‐terminal 129 SEC14p residues are sufficient to direct a catalytically inactive form of rat PI‐TP to the Golgi and provide the first evidence to indicate that a mammalian PI‐TP can stimulate Golgi secretory function in vivo.

Multiple organ dysfunction syndrome: Role of xanthine oxidase and nitric oxide

Abstract In general, the simple concepts first proposed over a decade ago for the role of xanthine oxidase (XO) in pathophysiolgy are no longer sufficient. This review summarizes evidence that has led to a resurgence in interest of XO physiology and pathology and in particular, data that implicates XO and nitric oxide (⋅NO) in the development of multiple organ dysfunction (MODS) following various pathologic states. The challenge for the next few years will be to define the precise mechanisms that XO plays in normal physiology and pathology. Although it has long been recognized that XO can produce oxidants, the significance of XO-generated oxidants extends beyond the concept of the intracellular generation of cytotoxic oxidants. It has been demonstrated that XO can be released into the circulation from cells and tissues with high intracellular XO specific activity following I/R, sepsis, burns, acute viral infection, and hemorrhagic shock. Once in the plasma the conversion to XO is rapid ( β , TNF- α , and TGF- β 1), in part, through activation of nuclear transcription regulatory factors. There also appears to be regulation of the vasoactive actions of ⋅NO by XO-generated oxidants to decrease rates of O 2 ⋅− generation, thus potentiating ⋅NO-mediated vasorelaxation. This regulation may be due to the reaction of ⋅NO with O 2 ⋅− to form ONOO − . Nitric oxide may also regulate O 2 ⋅− production post-transcriptionally by binding to the XO iron–sulfur moiety, sulfhydryl groups, or by reversible alteration of the flavin prosthetic site, thereby inhibiting activity. It is becoming apparent that tissue injury in MODS resulting from various pathologic states, including I/R, is the consequence not only excess production of reactive oxygen and nitrogen species (ROS and RNS) and their reaction with biologic target molecules, but also the effect of these oxidants in regulation of proinflammatory and anti-inflammatory mediators. The interplay of XO-generated oxidants and ⋅NO, has significant effects on cellular metabolism and organ function with their precise role in MODS requiring further elucidation. In summary, evidence was presented in this review that: (a) reactive species (ROS) are critical mediators of remote tissue injury; (b) ⋅NO and ⋅NO-derived oxidants contribute to the remote tissue damage; (c) XO, while a significant intracellular source of O 2 ⋅− ; is released into the circulation, binds, and concentrates on vessel walls to become a functionally critical source of oxidants even in tissues with low XO specific activity; and (d) that the balance between ⋅NO and O 2 ⋅− production determines whether the proinflammatory or anti-inflammatory properties are manifested.

Mechanistic insights relevant to protein secretion in yeast

During the past year, a powerful combination of genetic and biochemical approaches has yielded fascinating information with respect to the question of how proteins cross membranes and subsequently traffic between intracellular compartments of the yeast secretory pathway. Fundamental advances have been made in two specific areas. These include experiments that have provided new perspectives with respect to the nature of the soluble machinery involved in facilitating protein traffic from the cytoplasm to the lumen of the endoplasmic reticulum, and work that has provided a biochemical description of what may in effect represent a membranous ligand-gated channel that is required for protein translocation into the endoplasmic reticulum lumen.