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Biomedical subjects

M L McCullough

Publications and source records attributed to M L McCullough.

31 records · Page 2Linked to original sources
PubMed1998

Example of 2:1 interlimb coordination during fictive rostral scratching in a spinal turtle.

The usual interlimb coordination pattern during fictive rostral scratching in turtles is 1:1 coordination. We describe an example in a turtle of 2:1 coordination during fictive rostral scratching in which there were two cycles of ipsilateral hip flexor activity during each cycle of contralateral hip extensor activity. During 2:1 coordination, there were fluctuations in the ipsilateral hip flexor cycle period such that a larger ipsilateral hip flexor normalized period, which was associated with the onset of a contralateral hip extensor burst, alternated with a smaller ipsilateral hip flexor normalized period, which was associated with the absence of the onset of a contralateral hip extensor burst. These observations support the concept that contralateral circuitry modulates the timing of ipsilateral motor rhythms and therefore contributes to the production of the ipsilateral motor pattern for rostral scratching.

Animals↗
PubMed1991

The primary structures of four subunits of the human, high-molecular-weight proteinase, macropain (proteasome), are distinct but homologous.

Macropain (proteasome) is a high-molecular-weight proteinase complex composed of at least 13 electrophoretically distinct subunits. Previous work, including peptide mapping and limited amino acid sequencing, suggested that most of the subunits belong to an evolutionarily related group of different gene products (Lee et al. (1990) Biochim. Biophys. Acta. 1037, 178-185). In order to define the extent and pattern of subunit relatedness, and to determine the structural basis for possible similarities and differences in subunit functions, we are deducing the primary structures of macropain subunits by cDNA cloning and DNA sequence analysis. We report here the primary structures of four subunits. The data clearly demonstrate that the proteins represent different, but homologous gene products. Surprisingly, no evidence for homology with any other protein, including proteinases, was obtained. These results suggest that macropain is comprised of a previously unidentified family of evolutionarily related polypeptides. Because biochemical data indicate that macropain contains several different proteinase activities, the current results raise the possibility that the macropain complex is composed of a group of novel proteinases, distinct from those of other structurally identifiable proteinase families.

Amino Acid Sequence↗
PubMed1991

ATP-stimulated degradation of endogenous proteins in cell-free extracts of BHK 21/C13 fibroblasts. A key role for the proteinase, macropain, in the ubiquitin-dependent degradation of short-lived proteins.

Baby hamster kidney (BHK) 21/C13 cell proteins, labeled with [35S]methionine, [14C]leucine or [3H]leucine in intact cells, were degraded in soluble, cell-free extracts by an ATP-stimulated process. The stimulatory effect of ATP appeared to require ATP hydrolysis and was mediated to a large extent by ubiquitin. Although the cell extracts contained endogenous ubiquitin, supplementation with exogenous ubiquitin increased ATP-dependent proteolysis by up to 2-fold. Furthermore, antibodies against the E1 ubiquitin conjugating enzyme specifically inhibited both conjugation of [125I]ubiquitin to endogenous proteins and ATP/ubiquitin-dependent proteolysis. Addition of purified E1 to antibody-treated extracts restored conjugation and proteolysis. Proteins containing the amino acid analogues canavanine and azatryptophan were also degraded in vitro by an ATP/ubiquitin-dependent process but at a rate up to 2-fold faster than normal proteins. These results indicate that soluble, cell-free extracts of BHK cells can selectively degrade proteins whose rates of degradation are increased in intact cells. Treatment of cell-free extracts with antibodies against the high molecular weight proteinase, macropain, also greatly inhibited the ATP/ubiquitin-dependent degradation of endogenous proteins. Proteolysis was specifically restored when purified macropain L was added to the antibody-treated extracts. Treatment of cell extracts with both anti-macropain and anti-E1 antibodies reduced ATP/ubiquitin-dependent proteolysis to the same extent as treatment with either antibody alone. Furthermore, proteolysis could be restored to the double antibody treated extracts only after addition of both purified E1 and macropain. These results provide strong evidence for an important role for macropain in the ATP/ubiquitin-dependent degradation of endogenous proteins in BHK cell extracts.

Adenosine Triphosphate↗
PubMed1991

Feasibility of outpatient electrolyte balance studies.

Clinical studies requiring controlled electrolyte balance have traditionally been conducted in an inpatient (IP), metabolic ward setting. The purpose of this study was to test the feasibility of performing such studies in an outpatient (OP) clinical research setting. Focusing on sodium (Na) and potassium (K) balance, we retrospectively compared 28 subjects studied as OP vs 25 studied as IP on our metabolic ward. We assessed their adherence to our metabolic diets and their compliance with serial 24-hr urine collections. Dietary compliance was assessed by checksheet and urinary Na excretion; urine collection accuracy was determined by serial 24-hr creatinine excretion. The diets for both studies contained a low Na phase (10 mEq) and a high Na phase (200 mEq for IP and 250 mEq for OP), each lasting 1 week. When in balance on the low Na diet, 24-hr Na excretion was 4.6 +/- 0.7 mEq for OP and 13.4 +/- 2.2 mEq for IP, indicating excellent compliance with the low salt diet. Na excretion on the high Na diet was 184.5 +/- 7.4 mEq for OP and 195.3 +/- 9.6 mEq for IP. These values were not significantly different from each other; however, the OP were significantly less than their diet of 250 mEq Na (p less than 0.05). This difference may have been due to dermal Na losses. K excretion was also similar in the two groups. There was no significant difference in the reproducibility of individual multiple urinary creatinine measurements in OP vs IP.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

The high molecular weight multicatalytic proteinase, macropain, exists in a latent form in human erythrocytes.

The high molecular weight multicatalytic proteinase, macropain, has been purified from human erythrocytes in two forms that differ in caseinolytic activity up to 100-fold. Each form has a native molecular weight of 600,000 and is composed of a number of subunits ranging in molecular weights from 35,000 to 21,000. Although the two proteinase forms share a number of electrophoretically indistinguishable subunits, there are also subunits unique to the respective forms. The less active proteinase represents a latent enzyme because it was fully activated by two procedures including dialysis against water and pretreatment with low concentrations of sodium dodecyl sulfate. These procedures caused differential changes in the caseinolytic and two peptidase activities of the proteinase. An Mr 35,000 subunit, characteristic of latent macropain, is immunologically related to at least one of the other components of active macropain and disappeared after proteinase activation by dialysis. Nevertheless, loss of this subunit was not the cause of the increased activity. These results suggest that the proteolytic activity of cells may be regulated by the activation of the latent form of macropain.

Caseins↗
PubMed1989

ATP-dependent mechanisms for protein degradation in mammalian cells.

The biochemical basis for ATP-dependent protein degradation observed in intact cells has been studied in cell-free extracts of baby hamster kidney fibroblasts. ATP plays at least two distinct roles in proteolysis. First, ATP is required for the covalent conjugation of ubiquitin to protein substrates. This modification markedly enhances the rates of degradation of some, but not all, proteins. Second, ATP appears to stimulate the activity of a protease capable of degrading both ubiquitinated and non-ubiquitinated proteins. This protease has several biochemical and catalytic features that resemble those of the previously described high molecular weight protease, macropain. Furthermore, antibodies against highly purified human erythrocyte macropain inhibit both ubiquitin-dependent and ubiquitin-independent pathways of ATP-dependent proteolysis. Such results provide evidence for an important role for macropain in ATP-dependent proteolysis in mammalian cells.

Adenosine Triphosphate↗
PubMed1987

Metabolic bone disease in home total parenteral nutrition.

Home total parenteral nutrition (HTPN) is in its infancy but has proved to be lifesaving for patients unable to manage on enteral nutrition alone. However, this mode of nutrition therapy is not without problems. Aside from mechanical and other metabolic complications, a peculiar metabolic bone disease has been reported to occur in some HTPN recipients. The disease, characterized by abnormalities in calcium and phosphorus homeostasis, often results in osteomalacia, bone pain, and fractures. Reports of approximately 50 cases of metabolic bone disease have been published by centers in the United States and Canada. Factors that have been implicated as possible causes include infusion of excess vitamin D, aluminum, calcium, protein, or glucose; cyclic vs. continuous TPN administration; and the patient's previous nutritional state. Although removal of vitamin D or aluminum from the TPN solution and discontinuation of TPN altogether have been associated with improvement in symptoms, histology, and laboratory values, no single factor has been identified as the cause of this troubling phenomenon.

Bone Diseases, Metabolic↗
PubMed1976

The behavioral effects of prenatal hypoxia in the rat.

Pregnant rats were exposed to an oxygen depleted atmosphere (13% oxygen in nitrogen) at normal pressure in 2-hr daily sessions extending over approximately the last 14 days of pregnancy. Their progeny were compared with control progeny in terms of age of eye-opening, open-field behavior, and Hebb-Williams maze problem solving ability. The groups were not distinguishable by their performance in the open-field, but the experimental animals opened their eyes significantly earlier and made significantly more errors on Hebb-Williams maze problems.

Animals↗