The molecular defect of albumin Tagliacozzo: 313 Lys----Asn

Albumin Tagliacozzo is a fast-moving genetic variant of human serum albumin found in 19 unrelated families. The protein was isolated from the serum of a heterozygous healthy subject. Analysis of CNBr fragments by isoelectric focusing allowed us to localize the mutation to CNBr fragment IV (residues 299-329). This fragment was isolated on a preparative scale and subjected to tryptic digestion. Sequential analysis of the abnormal tryptic peptide, purified by RP-HPLC, revealed the variant was caused by 313 Lys----Asn substitution, probably due to a point mutation in the structural gene. The lack of a lysine residue accounts for the electrophoretic behavior of albumin Tagliacozzo.

Structural characterization of a chain termination mutant of human serum albumin

Mutant forms of human serum albumin have been detected on the basis of their abnormal electrophoretic mobility which is either faster or slower than that of normal albumin. In the present work we have studied the structure of a slow variant, referred to as albumin Ge/Ct, in order to define the cause of its genetic abnormality. The protein was isolated from the serum of a young healthy woman homozygous for the variant. Analysis of CNBr fragments by isoelectric focusing allowed us to localize the mutation to the COOH-terminal region of the molecule (residues 549-585). This fragment was isolated on a preparative scale and subjected to tryptic digestion. All tryptic peptides were purified by reverse-phase high performance liquid chromatography and characterized. Sequential analysis of three abnormal peptides revealed that albumin Ge/Ct has a shortened chain with the following COOH-terminal sequence: Leu-Val-Ala-Ala-Ser-Lys580-Leu-Pro. The presence of an additional lysine residue accounts for the electrophoretic behavior of the variant. It is likely that the variant may be caused by a single base deletion in the structural gene, a Cyt in mRNA codon 580, and the consequent shift in reading frame.

Immunological reactivity of native and modified alcohol dehydrogenase (ADH)

The extent to which treatment of horse liver alcohol dehydrogenase (ADH) by procedures known to disturb the Zn association induced conformation changes detectable by immunological techniques has been investigated. Treatment of ADH by sodium dodecyl sulphate or by total reduction and carboxymethylation leads to complete loss of reactivity with a rabbit immune serum against the native enzyme. After selective carboxymethylation the enzymatic activity was reduced but the preparation had the same immunological activity of the native enzyme. Similar results were obtained when ADH was treated with reagents known to react with the "functional" Zn atoms, such as sodium dietyldithiocarbamate, 1,10 phenanthroline, and 2,2' bipyridine. In contrast dialysis in 0.01M phosphate buffer containing 0.1mM EDTA removing the "structural" Zn atoms leads to a parallel decrease of enzymatic and immunological activity. Thus loss of "structural" Zn atoms affects the immune reactivity of ADH differently from the loss of "functional" Zn atoms.

Apparent subunit heterogeneity of NAD-dependent glyceraldehyde-3-phosphate dehydrogenase from spinach leaves

NAD dependent glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12) from spinach leaves has been previously investigated: the enzyme, homogeneous on conventional chromatography and analytical disc electrophoresis, shows on denaturing condition, non identical subunits of 37,000 and 14,000 daltons which have been separated in equimolar amounts after sodium dodecyl sulphate treatment (Speranza and Gozzer, 1978). Affinity chromatography carried out on these enyzme preparations allowed to separate a fully active enzyme of 150,000 daltons M.W. from a protein of 70,000 daltons M.W. which is devoid of glyceraldehyde-3-phosphate dehydrogenase activity: the purified enzyme shows 37,000 daltons subunits, while the second protein is made up of 14,000 daltons subunits. It is also reported that the 70,000 daltons protein could be separated from the enzyme by selective crystallization in the presence of organic solvents. It is concluded that the NAD-dependent glyceraldehyde-3-phosphate dehydrogenase from spinach leaves, as the homologous enzyme from other sources, is a tetramer of 37,000 daltons subunits.

Subunit structure and activity of glyceraldehyde-3-phosphate dehydrogenase from spinach chloroplasts

Glyceraldehyde-phosphate dehydrogenase (D-glyceraldehyde-3-phosphate : NADP+ oxidoreductase (phosphorylating), EC 1.2.1.13) from spinach chloroplasts is a polymeric protein of approx. 600,000 daltons and sodium dodecyl sulphate gel electrophoresis shows that it consists of two subunits of molecular weight 43,000 and 37,000. Comparison of amino acid analyses and tryptic peptide maps indicates that the two subunits have a different primary structure. The native enzyme contains 0.5 mol of NADP+ and 0.5 mol of NAD+ per protomer of 80,000 daltons, no reduced pyridine nucleotides have been detected. Almost complete inactivation is obtained by reaction of two cysteinyl residues per 80,000 daltons with tetrathionate or iodo[14C2]acetic acid; since the same amount of radioactivity is incorporated in the two subunits it is likely that they are both essential for the catalytic activity. Charcoal stripping of native glyceraldehyde-phosphate dehydrogenase produces an apoprotein which still retains most of the enzymatic activity but, unlike the holoenzyme, is gradually inactivated by storage at 4 degrees C and does not react with iodoacetate under the same conditions in which the holoenzyme is completely inactivated.

A structural study of pig liver glyceraldehyde-3-phosphate dehydrogenase

A substantial portion of the primary structure of pig liver glyceraldehyde-3-phosphate dehydrogenase has been investigated and the results compared with those previously reported for the pig muscle enzyme. Liver and muscle glyceraldehyde-3-phosphate dehydrogenases show the same amino acid content, and the first N-terminal residues occur in the same sequence. No differences in N-terminal residues and amino acid composition have been evidenced by analysis of several tryptic peptides, which account for about 50% of the total amino acid sequence. From the electrophoretic mobilities of peptides T8 T9 and T25 it is concluded that residues Asp 60, Asp 67 and Glu 220 in the reported sequence of the pig muscle enzyme must be present as amides in the liver enzyme. The NAD+ content was found to be 2 mol per tetramer, while higher values have been reported for the muscle enzyme from various mammalian sources. The reactivity of lysyl side chains towards pyridoxal 5'-phosphate has been examined: the results indicate that Lys 212 is the main site reacted in fully inactivated pig liver holoenzyme. A similar result has been found for rabbit muscle apoenzyme, whereas rabbit muscle holoenzyme reacts at Lys 212 and 191.