Methionine residues in peptides and proteins were oxidized to methionine sulfoxides by mild oxidizing reagents such as chloramine-T and N-chlorosuccinimide at neutral and slightly alkaline pH. With chloramine-T cysteine was also oxidized to cystine but no other amino acid was modified; with N-chlorosuccinimide tryptophans were oxidized as well. In peptides and denaturated proteins all methionine residues were quantitatively oxidized, while in native proteins only exposed methionine residues could be modified. Extent of oxidation of methionine residues was determined by quantitative modification of the unoxidized methionine residues with cyanogen bromide (while methionine sulfoxide residues remained intact), followed by acid hydrolysis and amino acid analysis. Methionine was determined as homoserine and methionine sulfoxide was reduced back to methionine. Sites of oxidation were identified in a similar way by cleaving the unoxidized methionyl peptide bonds with cyanogen bromide, followed by quantitative end-group analysis of the new amino-terminal amino acids (by an automatic sequencer).

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cDNA clones encoding the variable and constant regions of chicken immunoglobulin (Ig) gamma‐chains were obtained from spleen cDNA libraries. Southern blots of kidney DNA show that the variable region sequences of eight cDNA clones reveal the same set of bands corresponding to approximately 30 cross‐hybridizing VH genes of one subgroup. Since the VH clones were randomly selected, it is likely that the bulk of chicken H‐chains are encoded by a single VH subgroup. Nucleotide sequence determinations of two cDNA clones reveal VH, D, JH and the constant region. The VH segments are closely related to each other (83% homology) as expected for VH or the same subgroup. The JHs are 15 residues long and differ by one amino acid. The Ds differ markedly in sequence (20% homology) and size (10 and 20 residues). These findings strongly indicate multiple (at least two) D genes which by a combinatorial joining mechanism diversify the H‐chains, a mechanism which is not operative in the chicken L‐chain locus. The most notable among the chicken Igs is the so‐called 7S IgG because its H‐chain differs in many important aspects from any mammalian IgG. The sequence of the C gamma cDNA reported here resolves this issue. The chicken C gamma is 426 residues long with four CH domains (unlike mammalian C gamma which has three CH domains) and it shows 25% homology to the chicken C mu. The chicken C gamma is most related to the mammalian C epsilon in length, the presence of four CH domains and the distribution of cysteines in the CH1 and CH2 domains. We propose that the unique chicken C gamma is the ancestor of the mammalian C epsilon and C gamma subclasses, and discuss the evolution of the H‐chain locus from that of chicken with presumably three genes (mu, gamma, alpha) to the mammalian loci with 8‐10 H‐chain genes.

The complete amino acid sequence of alcohol dehydrogenase of Thermoanaerobium brockii (TBAD) is presented. The S-carboxymethylated protein was cleaved at methionine residues (with cyanogen bromide) to provide a set of 10 nonoverlapping fragments accounting for 90% of the sequence. These fragments were then overlapped and aligned, and the sequence was completed by using peptides generated by proteolytic cleavage at lysine residues (with Achromobacter protease I). The protein subunit contained 352 amino acid residues corresponding to a molecular weight of 37,652. The sequence showed about 35% identity with that of the prokaryotic Alcaligenes eutrophus alcohol dehydrogenase and about 25% identity with any one of the eukaryotic alcohol/polyol dehydrogenases known today. Of these, only 18 residues (5%) are strictly conserved: 11 Gly, 2 Asp, and 1 each of Cys, His, Glu, Pro, and Val.