Peptides or proteins were hydrolyzed by vapors of 90% pentafluoropropionic acid or heptafluorobutyric acid at 90°C for various time periods. The hydrolyzate mixtures analyzed by both fastatom-bombardment and electrospray ionization mass spectrometry showed a series of C-terminal successive degradation molecular ions. The degradation reaction may be due to the selective formation of an oxazolone ring at the C-terminal amino acid, followed by hydrolytic removal of the C-terminal amino acid. The major side reactions were cleavages of the peptide bonds at the C side of the internal aspartic acid residue and the N side of serine residue.

Ferredoxin:thioredoxin reductase is a [4Fe-4S] protein involved in the light regulation of carbon metabolism in oxygenic photosynthesis. This enzyme catalyses the reduction of thioredoxins with light-generated electrons. Ferredoxin:thioredoxin reductase is composed of two dissimilar subunits, a catalytic subunit, and a variable subunit. The catalytic subunit of spinach ferredoxin:thioredoxin reductase, which contains the redox-active disulfide bridge, was sequenced by conventional protein sequencing techniques and the functional roles of all eight cysteine residues were examined by chemical modifications. The polypeptide chain with a calculated molecular mass of 12,959 Da consists of 113 amino acids and has a calculated isoelectric point of 5.30. Six of the eight cysteine residues are clustered as Cys-Pro-Cys and Cys-His-Cys groups. Cys19 and Cys27 are free cysteines with no catalytic function, Cys54 and Cys84 constitute the redox-active disulfide bridge of the active site, and the remaining four, Cys52, Cys71, Cys73, and Cys82 bind the Fe-S cluster.

Ferredoxin:thioredoxin reductase (FTR) is an iron‐sulfur protein, which, in the presence of ferredoxin and thioredoxin, catalyses the light‐dependent activation of several photosynthetic enzymes. Spinach FTR consists of two dissimilar polypeptide chains, A and B, present in equal amounts. Whereas subunit B seems to be responsible for the catalytic activity, subunit A has no known catalytic function. We found earlier that the N‐terminus of subunit A, also called the variable subunit, shows terminal redundancy and that 2–3 of its serine residues are phosphorylated [Tsugita, A. Yano, K., Gardet‐Salvi, L. & Schürmann, P. (1991) Protein Sequence Data Anal. 4, 9–13]. We now report the complete amino acid sequence of subunit A, determined by conventional protein sequencing methods. The polypeptide chain with a calculated molecular mass of 12 669 Da consists of 112 amino acids and has a calculated isoelectric point of 5.4. The analysis of the sequence supports the idea that this subunit has no catalytic function. The comparison with a known cyano‐bacterial FTR reveals about 58% similarity and the striking presence of a N‐terminal extension in the spinach protein. This extension may be responsible for the reported size variability of this subunit.

Immunoreactive kallikrein has been demonstrated in the neurons of both prenatal and adult rat brains. However, the preferential site is quite different between the prenatal and adult brains, i.e., the former is mainly in the nuclei, and the latter is in the cell bodies and processes. In this study, the intensity of kallikrein mRNA expression was investigated in prenatal and postnatal rat brains by reverse transcription polymerase chain reaction (RT-PCR). A marked progressive increase in kallikrein mRNA expression was observed during the prenatal and early postnatal stage, with the maximum level at postnatal days 0 and 1 (P0 to P1). This helps to explain the previous immunohistochemical findings in which a strong immuno-intensity of kallikrein in the neurons of prenatal and newborn rat brains was found as compared with adult rats. The function(s) of kallikrein expressed in the neurons in the developing stages is unclear, but the role(s) must be different from that of the adult because of the unequivocal difference in its location between them. It is thus possible that kallikrein has certain unknown important role(s) in the neuronal physiology acting on nuclear protein(s) in the developing stages, although the possibility of function via kinin receptors cannot be excluded at present.