Search

Based on the findings obtained a conclusion was reached that cryosurgery is a worth-while exercise in patients of child-bearing age as a method enabling the menstrual function to be preserved. Electrodestruction of endometrium is to be targeted to patients of perimenopausal age to achieve amenorrhea. The aim of the above policy of managing patients is to enhance efficacy of treatment of hyperplastic processes in endometrium.

X-ray study of chicken cytosolic aspartate aminotransferase revealed conformational changes in the protein of two kinds: (1) a shift of the small domain adjacent to substrate-binding area due to interaction of the protein with two carboxyl groups of substrate and (2) a change in inclination of the coenzyme plane due to replacement of C = N bond of the coenzyme with Lys-258 by C = N bond with a substrate. An asymmetry in subunit behaviour is observed in both cases: the domain is shifted in one subunit and the coenzyme is rotated in other. Substrate-binding properties of each subunit are strictly dependent on the protein conformation in substrate-binding area.

The growth hormones (GHs) are polypeptide hormones with molecular weight of 22 kD consisting of one chain. GHs are synthesized in an anterior lobe of hypophysis as a precursors with molecular weight of 25 kD. These hormones are necessary for the normal growth and development of organism and play an essential role in regulation of anabolic processes. The characteristic features of GHs are species specificity and multiple biological activity. Cloning and sequencing of DNA complementary to the rat GH messenger RNA in 1977 represented one of the first mammalian cDNA to be analyzed (Seeburg et al, 1977). Since then a variety of cDNAs corresponding to members of GH family from different vertebrates have been isolated and analyzed. These cDNAs have been used to produce the hormones in bacteria and eucaryotic cells by recombinant DNA techniques.

The paper describes a method for producing gram-scale quantities of beef pancreatic ribonuclease A (RNase A) (EC 3.1.4.22) from commercial, amorphous and crystalline RNases. The method involves enzyme purification by chromatography on SP-Sephadex G-25, rechromatography on Bio-Rax 70 followed by concentration, storage and desalting in optimal conditions. In their properties the resultant preparations of RNase A are not inferior to the best commercial samples of the enzyme.

Previous comparison of amino acid sequences and three-dimensional structures has shown that the microbial ribonucleases from an evolutionarily related family that is separate from that of the pancreatic ribonucleases (Hill et al., 1983). The microbial and pancreatic ribonucleases catalyse the same two step hydrolysis of RNA via a cyclic 2′3′ intermediate. However, the specificities are different; the microbial enzymes prefer a purine base on the 3′ side of the scissile phosphate, and in some cases are very guanine specific.

The physico-chemical properties have been studied of RNase A selectively modified at the E-NH2-group of Lys-7 and Lys-41 with pyridoxal-P. Modification did not affect conformational stability of the protein globule, thus all changes in the molecule of the modified RNase A were localised around the alkylated Lys residue. In the both cases pyridoxyl-P. The residue was shown to be localized in the active site region of the (P-Pxy)-Lys-7-RNase A and its chromophore parts was highly exposed to the solvent. (P-Pxy) E-Lys-7-RNase A and its chromophore parts was highly exposed to the solvent. In the Lys-41 derivative, pyridoxamine-P was situated exactly in the active site and is partially hidden in the protein grobule. The pH-dependence of absorption spectra indicates that the chromophore of pyridoxyl-P in modified proteins is quite sensible to the ionic state of its surrounding. The usefulness of pyridoxyl-P as a reporter group was proved in the study with (P-Pxy)-Lys-7-RNase A. Some conformational changes involving His-119 were shown to take place in the course of the enzyme-nucleotide complex formation.

Structural aspects of specificity and catalytic activity of enzymes are studied on various objects, in particular on ribonucleases. Remarkable progress has been achieved in understanding the pyrimidine specificity of RNAse A at molecular level. The tertiary structures of different microbial ribonucleases were solved at atomic resolution recently (Hill et al., 1983). These enzymes belong to the so-called guanyl-specific RNases such as the well-known RNAse T1, which degrades single-stranded RNA to give oligonucleotides with terminal 3′ guanosine monophosphate. In many of these, the cleavage occurs as a two-step mechanism via 2′, 3′ cyclic nucleotide intermediates. In order to reveal molecular bases for substrate specificity of RNAse T1 the structures of the RNAse T1-2′-or 3′-GMP complex were studied at 2 A resolution (Heinemann and Saenger, 1982; Sugio et al., 1985). Some important features of recognition patterns were obtained from these data. However, it was not possible to draw cleancut conclusions in respect to the molecular mechanism for substrate discrimination. For this reason we have undertaken a study of the crystal structure of RNAse Pb1 (from Penicillium brevicompactum), a close analogue of RNAse T1.