Pyruvate kinase isozymic shifts of differentiating chick myogenic cells in vivo and in culture

Coordinate and discoordinate accumulation of protein constituents in chicken breast muscle

Accumulation of protein constituents in developing chicken breast muscle was examined by two-dimensional gel electrophoresis. Quantitative analysis of the two-dimensional gels showed a moderate coordination in accumulation among contractile proteins (actin, tropomyosin and myosin light chains) during postnatal development in spite of their isoform transition. Creatine kinase was also accumulated coordinately with contractile proteins during development. In contrast, accumulation kinetics of glycolytic enzymes (glyceraldehyde-3-phosphate dehydrogenase, aldolase and enolase) showed discoordination with those of contractile proteins. These findings suggest that there are two distinct phases in muscle maturation: (1) structural maturation and (2) metabolic maturation.

Expression of pyruvate kinase in astrocytes induced to differentiate in vitro

Astrocytes maintained in a chemically defined media undergo differentiation and a parallel increase in pyruvate kinase specific activity. These changes are accompanied by a shift in the isoelectrofocusing pattern, but not by expression of pyruvate kinase M4, the characteristic adult rat brain isozyme. Thus, this chemically defined media lacks a substance required to induce pyruvate kinase M synthesis and this function can be uncoupled from other aspects of cellular differentiation. The uncoupling of pyruvate kinase maturation from cellular differentiation and the observation of only a single, 2.3 kilobase, pyruvate kinase mRNA molecule at different stages of the postnatal development of rat brain support the concept that the K- to M-isoform transformation is a post-transcriptional event. The effect of the individual components of this chemically defined medium on pyruvate kinase specific activity was studied by eliminating one component at a time. The increase in activity was found to be completely dependent upon fibroblastic growth factor and prostaglandin F2 alpha and was partially dependent on the simultaneous presence of insulin.

Regulation of glycolytic enzyme RNA transcriptional rates by oxygen availability in skeletal muscle cells

Cytoplasmic beta-actin and five glycolytic enzyme cDNAs were isolated from a rat skeletal muscle cDNA library and together with a genomic clone of rat cytochrome c were used as probes to quantitate the respective RNA transcription rates in isolated nuclei run off transcription assays from stationary cells cultured under normal or 2% oxygen. The transcription rates of lactate dehydrogenase, pyruvate kinase, triosephosphate isomerase and aldolase increased by 2-5 fold during the 72 hr exposure to 2% oxygen. There was a small increase in actin RNA transcription while both cytochrome c and glyceraldehyde-3-phosphate dehydrogenase RNA transcription rates decreased. Since previous studies demonstrated an increase in steady state glyceraldehyde-3-phosphate dehydrogenase RNA during low O2 exposure it is concluded that the level of this RNA is regulated post transcriptionally whereas the other four glycolytic enzyme RNAs are regulated at least partially at the level of transcription by oxygen availability. The relative transcriptional rates of the RNAs in this study are related to their cellular RNA and protein concentrations.

Regenerating adult chicken skeletal muscle and satellite cell cultures express embryonic patterns of myosin and tropomyosin isoforms

Regenerating areas of adult chicken fast muscle (pectoralis major) and slow muscle (anterior latissimus dorsi) were examined in order to determine synthesis patterns of myosin light chains, heavy chains and tropomyosin. In addition, these patterns were also examined in muscle cultures derived from satellite cells of adult fast and slow muscle. One week after cold-injury the regenerating fast muscle showed a pattern of synthesis that was predominately embryonic. These muscles synthesized the embryonic myosin heavy chain, beta-tropomyosin and reduced amounts of myosin fast light chain-3 which are characteristic of embryonic fast muscle but synthesized very little myosin slow light chains. The regenerating slow muscle, however, showed a nearly complete array of embryonic peptides including embryonic myosin heavy chain, fast and slow myosin light chains and both alpha-fast and slow tropomyosins. Peptide map analysis of the embryonic myosin heavy chains synthesized by regenerating fast and slow muscles showed them to be identical. Thus, in both muscles there is a return to embryonic patterns during regeneration but this return appears to be incomplete in the pectoralis major. By 4 weeks postinjury both regenerating fast and slow muscles had stopped synthesizing embryonic isoforms of myosin and tropomyosin and had returned to a normal adult pattern of synthesis. Adult fast and slow muscles yielded a satellite cell population that formed muscle fibers in culture. Fibers derived from either population synthesized the embryonic myosin heavy chain in addition to alpha-fast and beta-tropomyosin. Thus, muscle fibers derived in culture from satellite cells of fast and slow muscles synthesized a predominately embryonic pattern of myosin heavy chains and tropomyosin. In addition, however, the satellite cell-derived myotubes from fast muscle synthesized only fast myosin light chains while the myotubes derived from slow muscle satellite cells synthesized both fast and slow myosin light chains. Thus, while both kinds of satellite cells produced embryonic type myotubes in culture the overall patterns were not identical. Satellite cells of fast and slow muscle appear therefore to have diverged from each other in their commitment during maturation in vivo.

Primary structure of chicken muscle pyruvate kinase mRNA

We have determined the cDNA sequence corresponding to chicken muscle pyruvate kinase mRNA; the predicted coding region spans 529 amino acids and establishes the complete amino acid sequence for the vertebrate enzyme. We demonstrate that the level of mRNA for this enzyme is under developmental control and suggest a structural model for the protein kinase-mediated regulation of the mammalian liver isozyme. We report a method for the direct analysis of, and the preparation of cDNA probes from, mRNA which has been fractionated on methylmercury/agarose gels.

Increase in sperm type hexokinase activity of rat spermatozoa during maturation

Rat hexokinases fro caput sperm (immature) and caudal sperm (mature) were investigated. The hexokinases from both sources were studied by DEAE-cellulose column chromatography and by cellulose acetate electrophoresis. The specific activity of caput sperm hexokinase was not significantly different from that of the caudal sperm enzyme. Spermatozoa possess two isozymes of hexokinase. Type I hexokinase was the predominant type in caput sperm whereas the sperm type of hexokinase was predominant in caudal sperm. Hexokinase types II and III were absent in both extracts.