protein
DEFINITION:
Any of a group of complex organic compounds which contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur, the characteristic element being nitrogen, and which are widely distributed in plants and animals. Proteins, the principal constituents of the protoplasm of all cells, are of high molecular weight and consist essentially of combinations of a-amino acids in peptide linkages. Twenty different amino acids are commonly found in proteins, and each protein has a unique, genetically defined amino acid sequence which determines its specific shape and function. They serve as enzymes, structural elements, hormones, immunoglobulins, etc., and are involved in oxygen transport, muscle contraction, electron transport, and other activities throughout the body, and in photosynthesis.
binding protein - any of a number of plasma proteins (See below) that bind to hormones of low solubility (chiefly the thyroid and steroid hormones), thus providing a transport system for them; some are specific for particular hormones, while others bind to any sparingly soluble hormones. Called also carrier protein or transport protein (See below).
carrier proteins - A binding protein (See above).
plasma proteins - The hundreds of different proteins present in blood plasma, including carrier proteins (such as albumin, transferrin, and haptoglobin), fibrinogen and other coagulation factors, complement components, immunoglobulins, enzyme inhibitors, precursors of substances such as angiotensin and bradykinin, and many other types of proteins.
transport protein - binding protein (See above).
tubule
DEFINITION:
A small tube.
arcuate renal tubule - A short, curved part of the distal end of the renal tubule (See below), extending from the distal convoluted tubule (See below) to the straight collecting tubule (See below). Called also junctional (connecting) tubule .
collecting tubule - A channel through which fluids pass from the secreting cells.
connecting tubule - Arcuate renal tubule (See above).
distal convoluted tubule - A distal, rolled-together or coiled part of the ascending limb of the renal tubule (See below), extending from the distal straight tubule (See below) to the junctional (connecting) tubule (See below).
distal straight tubule - Part of the renal tubule (See below) primarily on the ascending limb, extending from the thin tubule (See below) to the distal convoluted tubule (See above).
junctional (connecting) tubule - See arcuate renal tubule (above).
proximal convoluted tubule - The most proximal part of the renal tubule (See below), extending from the glomerular capsule to the proximal straight tubule (See below).
proximal straight tubule - Part of the descending limb of the renal tubule (See below), extending from the thin tubule (See below) to the distal convoluted tubule (See above).
renal collecting tubule - The arcuate renal tubule (See above), straight collecting tubule (See below), and papillary duct considered together. Called also collecting duct .
renal tubule - One of the minute, reabsorptive, secretory, and collecting canals, made up of basement membrane lined with epithelium, that form the substance of the kidneys. See also nephron .
straight collecting tubule - The lower straight part of the renal collecting tubule (See above), extending from the arcuate renal tubule (See above) to the papillary duct.
thin tubule - Part of the renal tubule (See above) at the lower end where the walls are especially thin; it extends from the proximal straight tubule (See above) to the distal straight tubule (See above). In juxtamedullary and deep cortical nephrons it makes up most of the length of Henle's loop.
protein
DEFINITION:
Any of a group of complex organic compounds which contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur, the characteristic element being nitrogen, and which are widely distributed in plants and animals. Proteins, the principal constituents of the protoplasm of all cells, are of high molecular weight and consist essentially of combinations of a-amino acids in peptide linkages. Twenty different amino acids are commonly found in proteins, and each protein has a unique, genetically defined amino acid sequence which determines its specific shape and function. They serve as enzymes, structural elements, hormones, immunoglobulins, etc., and are involved in oxygen transport, muscle contraction, electron transport, and other activities throughout the body, and in photosynthesis.
binding protein - any of a number of plasma proteins (See below) that bind to hormones of low solubility (chiefly the thyroid and steroid hormones), thus providing a transport system for them; some are specific for particular hormones, while others bind to any sparingly soluble hormones. Called also carrier protein or transport protein (See below).
carrier proteins - A binding protein (See above).
plasma proteins - The hundreds of different proteins present in blood plasma, including carrier proteins (such as albumin, transferrin, and haptoglobin), fibrinogen and other coagulation factors, complement components, immunoglobulins, enzyme inhibitors, precursors of substances such as angiotensin and bradykinin, and many other types of proteins.
transport protein - binding protein (See above).
protein
DEFINITION:
Any of a group of complex organic compounds which contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur, the characteristic element being nitrogen, and which are widely distributed in plants and animals. Proteins, the principal constituents of the protoplasm of all cells, are of high molecular weight and consist essentially of combinations of a-amino acids in peptide linkages. Twenty different amino acids are commonly found in proteins, and each protein has a unique, genetically defined amino acid sequence which determines its specific shape and function. They serve as enzymes, structural elements, hormones, immunoglobulins, etc., and are involved in oxygen transport, muscle contraction, electron transport, and other activities throughout the body, and in photosynthesis.
binding protein - any of a number of plasma proteins (See below) that bind to hormones of low solubility (chiefly the thyroid and steroid hormones), thus providing a transport system for them; some are specific for particular hormones, while others bind to any sparingly soluble hormones. Called also carrier protein or transport protein (See below).
carrier proteins - A binding protein (See above).
plasma proteins - The hundreds of different proteins present in blood plasma, including carrier proteins (such as albumin, transferrin, and haptoglobin), fibrinogen and other coagulation factors, complement components, immunoglobulins, enzyme inhibitors, precursors of substances such as angiotensin and bradykinin, and many other types of proteins.
transport protein - binding protein (See above).
protein
DEFINITION:
Any of a group of complex organic compounds which contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur, the characteristic element being nitrogen, and which are widely distributed in plants and animals. Proteins, the principal constituents of the protoplasm of all cells, are of high molecular weight and consist essentially of combinations of a-amino acids in peptide linkages. Twenty different amino acids are commonly found in proteins, and each protein has a unique, genetically defined amino acid sequence which determines its specific shape and function. They serve as enzymes, structural elements, hormones, immunoglobulins, etc., and are involved in oxygen transport, muscle contraction, electron transport, and other activities throughout the body, and in photosynthesis.
binding protein - any of a number of plasma proteins (See below) that bind to hormones of low solubility (chiefly the thyroid and steroid hormones), thus providing a transport system for them; some are specific for particular hormones, while others bind to any sparingly soluble hormones. Called also carrier protein or transport protein (See below).
carrier proteins - A binding protein (See above).
plasma proteins - The hundreds of different proteins present in blood plasma, including carrier proteins (such as albumin, transferrin, and haptoglobin), fibrinogen and other coagulation factors, complement components, immunoglobulins, enzyme inhibitors, precursors of substances such as angiotensin and bradykinin, and many other types of proteins.
transport protein - binding protein (See above).
Specialized transporter proteins; the products of two closely related genes, UT-A (Slc14a2) and UT-B (Slc14a1), modulate the movement of urea across cell membranes. To further examine the role of UT-A urea transporters in renal function we have selectively disrupted expression of the two known inner medulla collecting duct (IMCD) isoforms of UT-A, namely UT-A1 and UT-A3, producing UT-A1/3-/- mice. Knockout mice showed no evidence of UT-A1 or UT-A3 protein in the IMCD by both immunoblotting and immunocytochemistry, whereas expression of UT-A2 in the thin descending limbs of Henle’s loop was unchanged. Isolated perfused tubule studies of IMCDs from UT-A1/3-/- mice demonstrated a complete absence of phloretin-sensitive or vasopressin-stimulated urea transport with urea permeabilities similar to those calculated due to simple lipid phase diffusion. Analysis of growth by mouse weight revealed no differences between the genotypes and UT-A deficient mice had normal behavior, appearance and activity. On a 20% protein diet, and in comparison to littermate wild-type controls, UT-A1/3-/- mice exhibited significantly greater fluid consumption and urine flow. Under these conditions, UT-A1/3-/- urine osmolality was also significantly lower than wild-type mice. After a 24 hr water restriction, UT-A1/3-/- mice exhibited no ability to decrease urine flow and could not significantly raise their maximal urinary osmolality above that observed under basal conditions. Furthermore, during this 24 hr water restriction UT-A1/3-/- mice became lethargic and their body weight decreased by 21± 0.3% compared to 4.3 ± 1.2% in wild-type mice. The reduced concentrating ability observed was markedly diminished when urea excretion was decreased by dietary protein restriction (4% by weight), consistent with the Berliner hypothesis (1958) stating that the chief role of IMCD urea transport in the urinary concentrating mechanism is the prevention of urea-induced osmotic diuresis.