Prealbumin

Blake, C.C.F., et al. Structure of human plasma prealbumin at 2.5 A resolution. A preliminary report on the polypeptide chain conformation, quaternary structure and thyroxine binding. J. Mol. Biol. 88 1-12, 1974. 

Thyroxine (3, 5, 3,5-L-teraiodothyronine, T4) is a thyroid hormone, which is transformed in peripheral tissues by the enzyme 5 -monodeiodinase to triiodothyronine. T4 is 3-8 times less active than triiodothyronine. T4 circulates in plasma bound to plasma proteins (T4-binding globulin, T4-binding prealbumin and albumin). It is effective in its free non-protein-bound form, which accounts for less than 1%. Its half-life is about 190 h. 

Kaplan AP, Austen KF A prealbumin activator of prekallikrein. II. Derivation of activators of prekal-likrein from active Hageman factor by digestion with plasmin. J Exp Med 1971 133 696-712. 

Transthyretin (formerly prealbumin binds T4 and forms a complex with retinol-binding protein)... 

Patient s body weight ° Biochemical markers (e.g., prealbumin)... 

Thyroid hormone is liberated into the bloodstream by the process of proteolysis within thyroid cells. T4 and T3 are transported in the bloodstream by three proteins thyroid-binding globulin, thyroid-binding prealbumin, and albumin. Only the unbound (free) thyroid hormone is able to diffuse into the cell, elicit a biologic effect, and regulate thyroid-stimulating hormone (TSH) secretion from the pituitary. 

Prealbumin (trans- thyretin) 2-3 Binds triiodothyronine and to a lesser extent thyroxine carrier for retinolbinding protein Kidney dysfunction Cirrhosis, hepatitis, stress, inflammation, surgery, hyperthyroidism, cystic fibrosis, kidney dysfunction, zinc deficiency... 

Nitrogen balance Prealbumin or transferrin Serum triglyceride... 

Fig. 44. Stereo view of the prealbumin dimer. The black triangles are /9 bulges which help to turn outward the /S ribbons that form the loops proposed as a possible site for binding double-helical DNA.

Fig. 55. Two very similar 5-residue turns with a single a-helical hydrogen bond (a) pancreatic trypsin inhibitor residues 24-28, stabilized by the side chain of Asn-24 (b) prealbumin residues 18-22, stabilized by Asp-18.

The surfaces that form subunit-subunit contacts are very much like parts of a protein interior detailed fit of generally hydrophobic side chains, occasional charge pairing, and both side chain and backbone hydrogen bonds. Twofold symmetry is the most common relationship between subunits. The 2-fold is often exact and can be part of the actual crystallographic symmetry, as for the prealbumin dimer in Fig. 62. However, in many cases (e.g., Tulinsky et al., 1973 Blundell et al., 1972) individual side chains very close to the approximate 2-fold axis must take up nonequivalent positions in order to avoid overlapping (see Fig. 63). Conformational nonequivalence can extend further away from the axis and produce such effects as different... 

Fig. 62. A schematic drawing of the backbone of the prealbumin dimer, viewed down the 2-fold axis. Arrows represent p strands. Two of these dimers combine back-to-back to form the tetramer molecule.

A rather common feature of subunit contacts is ft sheet hydrogenbonding between strands in opposite subunits. Theoretically the relationship could be a pure translation or a 2-fold screw axis with a one-residue translation (for a pair of parallel strands), but all the known cases of intersubunit /3 sheet bonding turn out to be between equivalent strands related by a local 2-fold axis. For hydrogen-bond formation, the 2-fold must be perpendicular to the /3 sheet, requiring the two equivalent strands to be antiparallel. Those may be the only two /3 strands (as in insulin, Fig. 63), or they may be part of antiparallel P sheets (as in prealbumin, Fig. 62), or the rest of the sheets may be parallel (as in alcohol dehydrogenase domain 1). 

Trypsin-like serine proteases domains 1 and 2 Pyruvate kinase domain 2 Prealbumin Plastocyanin, azurin... 

Human 1-15 yr Hepatic Renal 13.5 29.5 (elevated serum prealbumin and transferrin) Li et al. 1993... 

Transport. A wellknown transport protein is hemoglobin in the erythrocytes (bottom left). It is responsible for the transport of oxygen and carbon dioxide between the lungs and tissues (see p.282). The blood plasma also contains many other proteins with transport functions. Prealbumin (transthyretin middle), for example, transports the thyroid hormones thyroxin and triiodothyronine. Ion channels and other integral membrane proteins (see p.220) facilitate the transport of ions and metabolites across biological membranes. 

The albumin fraction also includes transthyretin (prealbumin), which together with other proteins transports the hormone thyroxine and its metabolites. 

Amino Acid Systems Glutamine binding sites, 46, 414 labeling of the active site of r-aspartate /3-decarboxylase with yS-chloro-r-ala-nine, 46, 427 active site of r-asparaginase reaction with diazo-4-oxonorvaline, 46, 432 labeling of serum prealbumin with N-bro-moacetyl-L-thyroxine, 46, 435 a pyridoxamine phosphate derivative, 46, 441. 

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