Fluorescence banding in four species of Microtidae: an analysis of the evolutive changes of the constitutive heterochromatin

Three different fluorochrome and specific counterstain combination (DAPI/AMD, DA/DAPI and CMA/DA) treatments were applied to the chromosomes of four Microtidae (Rodentia) species. The results complete the data obtained in our previous paper (Burgos, M., Jiménez, R., & Dìaz de la Guardia, R., Genome 30:540–546, 1988) and prove that the changes in the constitutive heterochromatin in the evolution of the karyotypes of these species are not only due to gain or loss of heterochromatin, but are qualitative with respect to their nucleotide composition, repeated base pair organization or DNA-protein complex modification. These variations lead to the differential response to the fluorescence dye combinations used.     

Variable conservation of nucleolus organizer regions during karyotypic evolution in Microtidae

The location of the nucleolus organizer regions (NORs) was studied in four species of Microtidae (Microtus nivalis, M. cabrerae, M. arvalis, and Arvicola sapidus). The comparative study of these locations shows that some NORs have been conserved despite the chromosome rearrangements that have occurred through karyotypic evolution, while others have been lost. In addition, there are many chromosomes in which NORs seem to have appeared or been lost without apparent relation to the chromosome rearrangements. Some hypotheses regarding these facts are discussed in the text.     

Comparative study of G- and C-banded chromosomes of five species of Microtidae

G-banded karyotypes were compared in the following species of Microtidae: Microtus nivalis; M. cabrerae; M. arvalis and Arvicola sapidus. Previous observations on A. sapidus and A. terrestris (Díaz de la Guardia & Pretel, Caryologia 32: 183–189, 1979) were also incorporated in this study. The results show that Robertsonian translocations and pericentric inversions are common mechanisms involved in the karyotypic evolution of this group. Interspecific differences in C-banding patterns were also analyzed. Using the karyograph method (Imai et al., Am. Nat. 121: 477–488, 1983), the evolutionary distances of the karyotypes were estimated, and an attempt was made to establish a presumptive phylogenetic tree.     

Sequential homologies between procarboxypeptidases A and B from porcine pancreas

Automated Edman degradation of monomeric procarboxypeptidases A and B from porcine pancreas shows that their N-terminal regions (from residue 1 to 34-37) present a high degree of sequential homology to each other as well as to other related procarboxypeptidases. Conformational predictions based on these sequences confirm their structural homology and indicate the probable existence of two beta-turns, one beta-chain and a long alpha-helix in them. On the other hand, tryptic peptide maps on a reverse-phase column indicate great sequential similarities (if not identity) between monomeric procarboxypeptidase A and the procarboxypeptidase A subunit isolated from its binary complex with proproteinase E.     

The binding of [3H]oestradiol-receptor complex to hypothalamic chromatin of male and female mice

Histones and masking acidic proteins were removed from hypothalamic chromatin in order to evaluate/measure the number of available acceptor sites for the [3H]oestradiol-receptor complex. This number increases after dehistonizing and unmasking and is lower than published values for comparable preparations. No sex-related difference in [3H]oestradiol-receptor binding to hypothalamic chromatin in vitro was observed. Failure to observe such a difference suggests that sexual differentiation and steroid sensitivity cannot be attributed to marked differences in the degree of chromatin masking.     

A rapid, simple and reliable combined method for G-banding mammalian and human chromosomes

A simple and reliable method for G-banding chromosomes from human and mammalian cells is described. This rapid method combines hot saline and trypsin treatments and yields high quality G-bands in both bone marrow and cultured cells.     

Analysis of the activation process of porcine procarboxypeptidase B and determination of the sequence of its activation segment

The molecular events which lead to the proteolytic transformation of porcine procarboxypeptidase B (PCPB) in carboxypeptidase B (CPB) have been determined. Among pancreatic and other tested proteinases, trypsin is the only one capable of generating carboxypeptidase B activity from the zymogen, in vitro. In the first step of this process, trypsin produces cleavage at the boundary between the activation region and the CPB region. Subsequently, a definite sequence of cleavages occurs at the C-terminal end of the released activation segment of 95 residues, giving rise to characteristic intermediates and to a proteolytically resistant activation fragment of 81 residues. In this process, the newly formed CPB participates in the quick-trimming of the released activation peptides. Only a single CPB species is formed in the activation process. This fact and the inability of the released activation peptides to inhibit CPB--and, therefore, their inability to slow down the kinetics of appearance of CPB activity--are two important characteristics differentiating between the activation processes of procarboxypeptidases A and B. The sequence of the 95 residues (MW = 12,835) of the activation region of porcine PCPB has also been deduced, largely from the information obtained by Edman degradation of its fragments and in part by considerations of homology with the rat precursor. The porcine PCPB activation region contains a high percentage of acidic residues, lacks cysteines, methionines, and side-chain posttranslational modifications, and presents a low but significant homology (31%) with the corresponding sequence of porcine procarboxypeptidase A.     

Pigeon liver diacetyl reductase. Effects of pH on the kinetic parameters of the reaction.

(1) The pH dependence of the kinetic parameters of the reaction catalyzed by pigeon liver diacetyl reductase (EC 1.1.1.5) was investigated in the pH range 5.1-8.6. (2) From the results obtained it is postulated that: (a), a group of pK around 7, active in the protonated form, participates in the interaction of the enzyme with NADH and NAD. (b), a second group with a pK of 8.4, active in the protonated form too, takes part in the binding of diacetyl to E-NADH. (c) A third group of pK about 4.7-5, active in the unprotonated form, is involved at least in the dissociation of the complex E-NAD and in the attachment of diacetyl to E-NADH.     

Bovine skeletal muscle adenosine deaminase. Purification and some properties

A low molecular weight form of adenosine deaminase from bovine skeletal muscle was purified about 930-fold. The enzyme had a mol. wt of 31,000, a Km value for adenosine of 2.37 X 10(-5) M and a pH optimum at 7.0. This enzyme is very resistant to heat inactivation and does not require metal activators or other dialysable cofactors. A possible role in the post-mortem metabolism of adenine nucleotide in skeletal muscle is discussed.