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Biomedical subjects

R Calvert

Publications and source records attributed to R Calvert.

85 records · Page 5Linked to original sources
PubMed1978

Some properties of a Ca2+- and (or) Mg2+-requiring nucleoside di- and tri-phosphatase(s) associated with the membranes of rat pancreatic zymogen granules.

Membranes of rat pancreatic zymogen granules have been purified and found to be essentially free of contamination by mitochondria, microsomes, and plasma membranes. They possessed an acid phosphatase activity which derived probably from lysed lysosomes contaminating the purified zymogen granules from which the membranes were prepared. These membranes were found to contain a strong Ca2+- and (or) Mg2+-requiring activity toward all nucleoside di- and tri-phosphates. Various data support the tentative conclusion that a single protein catalyzes the hydrolysis of the nucleoside di- and tri-phosphates. This protein appears to be intrinsic with its active site localized on the internal face of the membranes.

Adenosine Triphosphatases↗
PubMed1975

Structure of rat ultimobranchial bodies after birth.

The evolution of ultimobranchial bodies in Holtzman rats during the first 64 weeks after birth was studied by reconstructing three-dimensional models from serial sections stained by the periodic acid-Schiff technique.Radio-autography with 125I was made to see if ultimobranchial cells and/or follicular cells lining the lumen of mixed follicles were able to iodinate proteins. The term ultimobranchial body designates herein an embryonic vesicular structure (derived from the third pharyngeal pouch) whose wall is made of stratified squamous epithelium. During the first week after birth, the vesicular ultimobranchial body elongates rapidly and becomes a canal or a duct. During the second week, cell desquamation brings about local dilatations in the lumen of these ducts; with further enlargement ultimobranchial follicles will appear. In one-day-old rats, mixed follicles are present. Only the follicular component of mixed follicles iodinates proteins as is shown by radioautography. The reconstructed models enlarge rapidly up to the 56th day after birth at which time their weight has increased nineteenfold. These same models show that the three morphological components of ultimobranchial parenchyma, namely ducts, follicles and mixed follicles, are in continuity within the thyroid parenchyma. The formation of new thyroid follicles after birth and the possiblility that the ultimobranchial parenchyma may function as an endocrine gland of holocrine type are discussed.

Age Factors↗
PubMedDate not supplied

Hemolysis by chrysotile asbestos fibers. I. Influence of the sialic acid content in human, rat, and sheep red blood cell membranes.

Complete removal of accessible sialic acids from human, rat, and sheep red cell membranes does not inhibit the hemolytic properties of chrysotile asbestos fibers. After 60 min of contact, the percentages of hemolysis are comparable between the treated and the nontreated groups. Nevertheless, with low concentrations of fibers the initial velocity of hemolysis of rat and sheep red blood cells is lower in the neuraminidase-treated group. Although sialic acids are not essential for the expression of the hemolytic activity of asbestos, we suggest that these acids could play a role during the first seconds or minutes of the hemolytic process by increasing the electrostatic attraction between the red blood cell membranes and the fibers. However, it is clear that asbestos fibers provoke hemolysis by acting on some other cell membrane component(s).

Animals↗