Two lectins with RNase activity obtained from eggs of Rana catesbeiana and R. japonica and RNase obtained from R. catesbeiana liver show 65-83% protein homology. The base specificity of these frog proteins was studied with 8 dinucleoside phosphates as substrates and 8 nucleotides as inhibitors. The base specificities of the B1 and B2 sites of these proteins are U greater than C and G greater than U greater than A, C, respectively. The three frog proteins are more resistant than RNase A to heat treatment, guanidine-HCl and pH-induced denaturation; i.e., they retain their native conformation up to at least 70 degrees C at pH 7.5. Differences in stability and base specificity among RNase A and the three frog proteins are discussed in relation to the primary structures. Although the two lectins agglutinate tumor cells (e.g., Ehrlich, S-180 and AH109A ascites carcinoma cells), the liver RNase has no such activity. Agglutination of AH109A cells by the two lectins is inhibited by nucleotides. Our results indicate that the agglutination sites are not identical with, but are related to, the active sites of the three frog proteins.
A pyrimidine base-specific ribonuclease was purified from bullfrog (Rana catesbeiana) liver by means of CM-cellulose column chromatography and affinity chromatography on heparin-Sepharose CL-6B, which gave single band on SDS-slab electrophoresis. The primary structure of the bullfrog liver RNase was determined. It consisted of 111 amino acid residues, including 8 half-cystine residues. From the sequence, it was concluded that three disulfide bridges in RNase A were conserved in the bullfrog RNase, that a disulfide bridge in RNase A [Cys65-Cys126 (RNase A numbering)] was deleted, and that a new disulfide bridge was created in the C-terminal part of the enzyme. In this frog RNase, the amino acid residues thought to be essential for catalysis in bovine pancreatic RNase A were conserved except for Asp121 (RNase A numbering). The sequence homology of the bullfrog liver RNase with bovine pancreatic RNase A was 30.6%. The sequence of bullfrog liver RNase was very similar to those of lectins obtained from bullfrog egg by Titani et al. [Biochemistry (1988) 26, 2189-2194] and R. japonica egg by Kamiya et al. [Seikagaku (in Japanese) (1989) 60, 733; and personal communication from Kamiya, Y., Oyama, F., Oyama, R., Sakakibara, F., Nitta, K., Kawauchi, H., and Titani, K.]. The sequence homology between the bullfrog liver RNase and the two lectins was 70.2 and 64.8%, respectively.
A 6-year-old boy started to receive oral prednisolone for an incipient nephrotic syndrome. Two weeks later, he started to receive a calcium antagonist because of hypertension. Another two weeks later, he was still not in complete remission; therefore a renal biopsy was performed, and a pathological diagnosis of focal segmental glomerulosclerosis syndrome was made. The day after the renal biopsy, his systolic blood pressure was in the 120 mmHg range, and he had impaired consciousness and conjugate deviation to the left. We diagnosed him with posterior reversible encephalopathy syndrome. Continuous intravenous infusion of nicardipine and that of midazolam were started, fosphenytoin and phenobarbital were administered, and continuous electroencephalogram monitoring was performed. After an electroencephalogram showed a decreasing tendency of spike-and-wave discharges, his consciousness recovered, and his imaging findings improved. An angiotensin-converting enzyme inhibitor was administered, and his systolic blood pressure fell to around 100 mmHg. Administration of prednisolone was tapered and discontinued, and his urine total protein to creatinine ratio (g/g•Cr) fell under 0.5. It is of note that pediatric patients with renal disease have many risk factors for posterior reversible encephalopathy syndrome and may develop it even in the absence of significant hypertension or immunosuppressive medication.
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