Flotation therapy for downer cows

Cattle that become recumbent (unable to get up) as the result of calving difficulty, low blood calcium, traumatic injuries, or other disorders are prone to develop subsequent pressure damage of muscles, nerves, and areas of skin. The resulting medical problems that are secondary to prolonged recumbency may be more life-threatening than the initial medical disorder that caused recumbency. Flotation therapy is an effective means of physical therapy for rehabilitation of downer cattle. A description of flotation therapy and data from the first year of use of the flotation tank at the Veterinary Medical Teaching Hospital, Kansas State University, are presented.; Dairy Day, 1996, Kansas State University, Manhattan, KS, 1996

A morphological view on mitochondrial protein targeting

Mitochondrial protein targeting includes both intramitochondrial sorting of proteins encoded by the organellar genome and import and subsequent sorting of nuclear encoded precursor proteins. Only a few proteins are encoded by the mitochondrial genome and synthesized in the organellar matrix. These include predominantly inner membrane proteins that are perhaps co-translationally inserted into this membrane. Biochemical data suggest that insertion into the inner membrane may be confined to the inner boundary membrane. Ultrastructurally, however, a preferential association of ribosomes with either inner boundary or cristae membranes has not been established. The majority of the mitochondrial proteins are nuclear encoded and synthesized as precursors in the cytosol. Electron microscopic studies revealed that import of precursor proteins is generally confined to sites where both mitochondrial envelope membranes are closely apposed. In line with these observations, biochemical studies indicated that precursor proteins destined for the inner membrane or matrix have to interact with the energized inner membrane to allow complete passage of the precursor through the outer membrane. As a consequence, the mitochondrial envelope membranes have to be in close proximity at protein import sites. In isolated mitochondria distinct sites (designated as contact sites) exist where both envelope membranes are closely apposed and presumably stably associated. In situ, however, mitochondrial boundary membranes are in close proximity over large areas that cover almost the entire mitochondrial periphery. Consequently, the relative area of the mitochondrial surface, where both boundary membranes are in sufficient proximity for allowing protein translocation, is generally larger in situ compared to that in isolated organelles. Immunocytochemical localization studies showed a rather random distribution of components of the mitochondrial protein translocation machinery over the entire mitochondrial surface and not confined to contact sites. Based on these ultrastructral data and recent biochemical findings we propose that mitochondrial protein import sites are dynamic in nature and include relatively labile regions of close association of the boundary membranes. In vitro, however, mitochondrial protein import may preferentially take place at or near the presumably stable contact sites

A dynamic model of the mitochondrial protein import machinery

Many proteins are translocated into or across two mem-branes in order to reach their functional destination; these include many nuclear-encoded mitochondrial and chloro-plast proteins, as well as proteins transported into or across the outer membrane of gram-negative bacteria. In eukaryotes, mechanistic insights have been obtained mainly with the mitochondrial two-membrane transport system. By generating translocation intermediates that span both mitochondrial membranes at the same time, it has been demonstrated that the outer and inner mem-brane translocation machineries cooperate in the import of preproteins (Hart1 and Neupert, 1990; Baker and Schatz, 1991). Translocation contact sites were defined as mito-chondrial import sites where the outer and inner mem-branes are so close together that they can be spanned b

Protein translocation across mitochondrial membranes

Protein translocation across biological membranes is of fundamental importance for the biogenesis of organelles and in protein secretion. We will give an overview of the recent achievements in the understanding of protein translocation across mitochondrial membranes(1-5). In particular we will focus on recently identified components of the mitochondrial import apparatus

Contact sites between inner and outer membranes

Contact sites between both mitochondrial membranes play a predominant role in the transport of nuclear-coded precursor proteins into mitochondria. The characterization of contact sites was greatly advanced by the reversible accumulation of precursor proteins in transit (translocation intermediates). It was found that the sites are saturable, apparently contain proteinaceous components and mediate extensive unfolding of the polypeptide chain in translocation. Some components of mitochondrial contact sites are currently being identified