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Biomedical subjects

M J White

Publications and source records attributed to M J White.

At least 91 records · Page 5Linked to original sources
PubMed1988

Implications of boundary choice for the measurement of residential mobility.

Analyses of residential mobility are usually conditioned on a system of geography in which territory is divided into discrete units. Types of movement are defined in terms of these units, the most important distinction being that between local mobility and migration. Here we examine explicitly the implications of the choice of the migration-defining boundary in the U.S. over the 1940-1980 period. We demonstrate how boundary choice influences the extent and character of selectivity of the mobile population by using demographic and social characteristics. It appears that over time the state line may be replacing the county line in distinguishing kinds of migrants. Further, our results point to a growing fraction of footloose migrants, not tied to local territory, identified by their migration history rather than demographic characteristics.

Adult↗
PubMed1987

How probable are antibody cross-reactions?

Antibodies to polypeptides are increasingly being used in research. Their specificity and tight but reversible binding make them ideal for applications such as identification of proteins, immunological quantification or purification, and peptide mapping. Antibodies are also used in medicine to deliver loads to specific sites in tissues, and in electron microscopy as heavy metal conjugates to locate antigens in thin sections. While these techniques depend on specificity of antibody binding, it is occasionally observed that cross-reactions occur. These cross-reactions are attributed to the existence of one or more antibody binding sites common to both polypeptides. It is important to know whether these cross-reactions are expected due to chance alone, or if they are improbable and likely due to some causative agent. Examples of such causative agents might include gene duplication events or convergence due to functional constraints. At the present time, good methods for predicting the probability and therefore the frequency of cross-reactions are unavailable. In this paper we apply some recently reported mathematical results to address the following questions: (1) What is the probability that polyclonal or monoclonal antibodies raised against a given polypeptide will cross-react with another polypeptide due to chance alone? (2) What is the probability that polyclonal or monoclonal antibodies raised against a given polypeptide will cross-react with one or more polypeptides in a pool of polypeptides? Approximate answers to these questions are presented for cases where amino acid compositions of linear polypeptides are known or unknown, but the amino acid sequence of one or more of the polypeptides is not known. Implications of the results for antibody use in protein research are discussed.

Amino Acid Sequence↗
PubMed1987

Polypeptides belonging to each of the three major chlorophyll a + b protein complexes are present in a chlorophyll-b-less barley mutant.

Polypeptides of the three major chlorophyll a + b protein complexes were detected in a chlorophyll-b-less barley mutant (chlorina f2) using immunological techniques. Antibodies to CP Ia, a photosystem I complex containing both the reaction center (CP I) and the chlorophyll a + b antenna (LHCI), detected substantial amounts of LHCI polypeptides in mutant thylakoids. Some polypeptides of the two photosystem-II-associated chlorophyll a + b complexes, CP 29 and LHCII, were also detected using antibodies raised against these complexes. The CP 29 apoprotein and the minor 25-kDa polypeptide of LHCII were present in amounts that could be seen by Coomassie blue staining. In contrast, the two major polypeptides of LHCII were greatly diminished in amount, and one of them may be completely absent. These data suggest that the absence of chlorophyll b may have differing effects on the synthesis, processing or turnover of the various chlorophyll a + b binding polypeptides. They also show that these polypeptides can be inserted into thylakoids in the absence of Chl b, and that significant amounts of some of them are accumulated in the mutant thylakoids.

Chlorophyll↗
PubMed1987

Antibodies to the photosystem I chlorophyll a + b antenna cross-react with polypeptides of CP29 and LHCII.

A chlorophyll (a + b)--protein complex associated with photosystem I (PSI) was isolated from a larger PSI complex (CPIa) produced by electrophoresis of barley thylakoids solubilized with 300 mM octyl glucoside. It had an apparent Mr of 35,000-43,000 on 7.5% and 10% acrylamide gels respectively, and a chlorophyll a/b ratio of 2.5 +/- 1.5. Denaturation released four polypeptides migrating between 21-24 kDa. They were well separated from the polypeptides of the two photosystem II chlorophyll a + b antenna complexes: LHCII (25-27 kDa) and CP29 (28-29 kDa). In order to study the PSI antenna complex, antibodies were raised against highly purified CPIa. The antigen appeared to be pure when electrophoresed, blotted and reacted with its antiserum, i.e. anti-CPIa detected only the 64-66-kDa CPI apoprotein and the four 21-24 kDa antenna polypeptides. However, when blotted against the whole spectrum of thylakoid proteins, it cross-reacted with both LHCII and CP29 apoproteins. Removal of anti-CPI activity from the anti-CPIa did not affect these cross-reactions, showing that they were not due to antibodies directed against CPI. To show that the same antibody population was reacting with both the photosystem I and photosystem II antenna polypeptides, anti-CPIa was adsorbed onto highly purified CPIa on nitrocellulose. The bound antibody was eluted and used again in a Western blot against whole thylakoid proteins. This selected antibody population showed the same relative strength of reaction with photosystem I and photosystem II antenna polypeptides as the original antibody population had. Similar observations have been made with antibodies to the two photosystem II antenna complexes. We therefore conclude that there are antigenic determinants in common among the chlorophyll a + b binding polypeptides, and predict that there could be amino acid sequence similarities.

Antibodies↗
PubMed1987

Production of long-chain alcohols by yeasts.

Fourteen yeast strains from six genera were analysed for the presence of long-chain alcohols. Six strains from three genera contained long-chain alcohols, highest levels being found in Candida albicans. The alcohols were identified and determined by TLC, GLC and GLC-MS. The major long-chain alcohols synthesized by these organisms were saturated, primary alcohols with C14, C16 or C18 chain length. Unsaturated long-chain alcohols were not detected. In all strains that produced long-chain alcohols, the relative proportions were C16 greater than C18 greater than C14. Long-chain alcohol contents were higher in organisms from anaerobically, as compared with aerobically, grown cultures reaching about 650 micrograms (g dry wt organisms)-1 in stationary-phase cultures of C. albicans. In cultures of C. albicans, synthesis of long-chain alcohols occurred only after the end of exponential growth. The alcohols were predominantly present as free alcohols. The fatty-acyl chain-length profile of the triacylglycerol and to a lesser extent the sterol/wax ester fractions from C. albicans reflected that of the long-chain alcohols produced by this yeast.

Alcohols↗
PubMed1987

Electrically evoked isokinetic plantar flexor torque in males.

The involuntary angle-specific isokinetic plantar flexor torques of seven male subjects aged 18-21 yr were measured using a Cybex II dynamometer (Lumex) modified by the addition of a strain-gauge load cell to improve the dynamic response of the instrument. Supramaximal electrical stimuli were used to evoke a maximal tetanic response from the triceps surae and ensure constant muscle activation at each angular velocity studied. Angle-specific torques were measured over a range (0.5-5.0 rad/s) of preset velocities, torque decreasing in a nonlinear manner with increasing angular velocity. The torque-velocity data was adequately described by an exponential equation of the form: V = a(e-1/b - e-Po/b) where V = velocity (rad/s), P = torque (N.m), Po = isometric torque (N.m), and a and b are constants. The mean intrasubject coefficient of variation of torque over the range of velocities studies was 7.9 +/- 1.88% (SD).

Adult↗
PubMed1986

Therapy of primary cutaneous melanoma.

The essential tenets of early recognition, biopsy, and appropriate surgical treatment of melanoma are reviewed. The controversies of elective regional lymph node dissection and isolated limb perfusion are discussed, as well as the newer modalities of immunotherapy.

Biopsy↗
PubMed1986

Mechanical properties of young and elderly human muscle.

The electrically evoked isometric properties of the triceps surae have been studied in young (22 yr) and elderly (69 yr) men and women. The results show that the triceps surae of elderly subjects had an increased time to peak tension (TPT) of the twitch, a lower specific tension (force/cross section area), and showed a greater relative force loss when subjected to a standard "fatigue" test procedure than young triceps surae. The respective figures for TPT, specific tension, and fatigue index (FI) were 147 +/- 15 ms (male), 143 +/- 8 ms (female), 19.5 N/cm2 and 0.52 +/- 0.16 (male), 0.37 +/- 0.09 (female) in the elderly, compared with 118 +/- 14 ms (male), 132 +/- 11 ms (female), 32.9 N/cm2 and 0.67 +/- 0.11 (male), 0.62 +/- 0.09 (female) in their younger counterparts. The peak rates of rise (delta P50, delta P200) and relaxation (delta PR50, delta PR200) of tetani at 50 Hz and 200 Hz were slower (p less than 0.05) in the elderly group. The delta P50 and delta P200 were inversely associated (r = 0.76 and -0.50 respectively) with TPT, and the half relaxation time (1/2RT) of the maximal twitch was related to delta PR50 (r = 0.53). The decrease of tetanus relaxation rate during the 2 min fatigue test (delta PRF) was greater in the elderly than the young and was positively associated (r = 0.74) with FI. It is concluded that elderly muscle is weaker, more slowly contracting and fatigable than that of the young. However, it is suggested that the reduced specific tension and enhanced fatiguability of the elderly may in part be due respectively to the inadequacies of our estimates of the effective cross-sectional area CSA) of contractile tissue in the lower leg and the influence of blood flow which may be compromised during a 2 min test.

Adult↗
PubMed1986

Segregation and diversity measures in population distribution.

"The purposes of the present paper are to show the relationship between measures of population diversity and measures of segregation, to describe the salient properties of these indexes, and to demonstrate the empirical interrelationships among them." Some measures not frequently used in population studies are considered, and empirical illustrations are given of the significance of using one measure rather than another. In particular, the author stresses proportional reduction of error interpretations for an index and considers its ability to handle more than two groups. The primary geographic focus is on the United States. The "introductory section of the paper treats conceptual issues in more detail. The second section reviews selected measures and recent critical viewpoints, while the third section tests their empirical performance. The conclusion makes some recommendations about the selection of an index. A detailed bibliography follows."

Americas↗
PubMed1986

Comparison of alternating to nonalternating chemotherapy regimens for non-small cell lung cancer.

Forty-seven patients with stage III lung cancer from four institutions in the Denver area were entered in a study comparing two regimens of chemotherapy. The patients were randomized into two groups: Group A received lomustine, cyclophosphamide, vincristine, cisplatin, and doxorubicin monthly; Group B received the five-drug regimen on Months 1, 3, and 5 and received 5-FU by constant infusion, methotrexate, and mitomycin on Months 2, 4, and 6. The age, extent of disease, Karnofsky score, prior therapy, and average number of chemotherapy courses received in each group were comparable. The median survival in Group A was 265 days and in Group B was 163 days (P greater than 0.25). There does not seem to be an advantage in survival in patients who are treated with the eight-drug regimen over the five-drug regimen.

Adenocarcinoma↗
PubMed1985

Adaptation of mechanical properties of muscle to high force training in man.

The first dorsal interosseus muscle of the hand was trained for 8 weeks using eighty maximal 10 s voluntary isometric contractions per day. As a result of this training the maximal voluntary force increased by 33%, but electrically evoked tetanic tension increased by only 11%. In other subjects the muscle was trained using electrical stimulation at 60 Hz to evoke eighty maximal 10 s tetani per day for 8 weeks. This training produced no increase in maximum voluntary force. Our results show that the increase in maximal voluntary force under these conditions may be due to a change in the voluntary neural drive to the muscle.

Adaptation, Physiological↗
PubMed1984

The effects of immobilization, after lower leg fracture, on the contractile properties of human triceps surae.

The contractile properties of the triceps surae were evaluated in 11 patients after unilateral fracture of the lower leg and subsequent immobilization for 135 +/- 68 days. Calf muscle cross-sectional area (plus bone: CSA) was assessed from anthropometric measurement. It was shown that the injured leg had a faster time to peak tension and increased half-relaxation time (1/2 RT); twitch force (Pt) was reduced by 25%. Evoked maximal tetanic tensions (Po) at 10 and 20 Hz were reduced by 51% and 46% respectively compared with the uninjured leg. The force of a maximal voluntary contraction (MVC) was also reduced, by 50%, but calf circumference and CSA were only 5% and 16% respectively lower in the injured leg. It was concluded that the changes in contractile speed may indicate a relatively greater atrophy of slow (type I) muscle fibres. The relationship between CSA and tension generation in the injured limb was shown to be poor after immobilization and during recovery. Anthropometric estimation of CSA does not appear to reflect the degree of muscle wasting, as indicated by reduced tension development after immobilization.

Adult↗
PubMed1984

The effects of short-term voluntary immobilization on the contractile properties of the human triceps surae.

In four male subjects one leg was immobilized in a full leg cast for 2 weeks. Measurements of the contractile properties of both triceps surae were made before, during and after immobilization. There was a significant increase in the mean twitch time to peak tension (Tc) after 1 week of immobilization from 126 +/- 10 ms to 143 +/- 20 ms (P less than 0.05) and in the half-relaxation time (T1/2r) from 88 +/- 7 ms to 107 +/- 12 ms (P less than 0.01). There were no further significant (P less than 0.1) changes in the twitch characteristics during the second week of immobilization. The strength of a maximal voluntary contraction (m.v.c.) declined by 11% (P less than 0.05) after 1 week and 24% (P less than 0.05) after 2 weeks. Twitch tension, tetanic tension and muscle fatigability were not significantly altered during immobilization. Muscle (plus bone) calf cross-sectional area (A) was reduced by 5% (P less than 0.01) after 1 week and a further 3% (P less than 0.05) after 2 weeks. The Tc and T1/2r of the twitch, m.v.c. and A returned to control values within 2, 7, 4 and 14 d respectively. No significant (P less than 0.01) changes were observed in the mechanical properties of the triceps surae of the contralateral limb during the period of immobilization. The results suggest that short-term voluntary immobilization is associated with atrophy and a diminished capacity of the muscle to develop maximal voluntary force.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗