Engineering topics

Mcpherson, Alexander

Publications and source records attributed to Mcpherson, Alexander.

4 records

NASA NTRS1992

Two approaches to the rapid screening of crystallization conditions

A screening procedure is described for estimating conditions under which crystallization will proceed, thus providing a starting point for more careful experiments. The initial procedure uses the experimental setup of McPherson (1982) which supports 24 individual hanging drop experiments for screening variables such as the precipitant type, the pH, the temperature, and the effects of certain additives and which uses about 1 mg of protein. A second approach is proposed (which is rather hypothetical at this stage and needs a larger sample), based on the isoelectric focusing of protein samples on concentration gradients of common precipitating agents. Using this approach, crystals of concanavalin B and canavalin were obtained.

Mcpherson, Alexander↗

NASA NTRS1991

The effect of microgravity on protein crystal growth

Based on the results of microgravity crystallization experiments using the protein canavalin aboard four separate U.S. Space Shuttle missions, visual observations and diffraction data are presented that support the contention that protein crystals of improved quality can be obtained in a microgravity environment. With canavalin, no significant increase in resolution was noted, but an overall improvement in diffraction quality, as judged by statistical analyses of the data, was clear. This improvement in quality may be due primarily to the elimination of defects and dislocations rather than an overall enhancement of order. The mechanism for this improvement may be microgravity-stabilized depletion zones that develop around growing crystals that establish and maintain optimal growth conditions more rapidly following nucleation. Such zones would be destroyed by convective flow effects in earth's gravity.

Mcpherson, Alexander↗

NASA NTRS1988

The use of heterogeneous and epitaxial nucleants to promote the growth of protein crystals

Fifty different mineral samples were tested as potential heterogeneous or epitaxial nucleants for four commonly crystallized proteins. It was found, using conventional protein crystallization techniques, that for each protein there was a set of mineral substrates that promoted nucleation of crystals at lower critical levels of supersaturation than required for spontaneous growth. In at least one case, the growth of lysozyme on the mineral apophyllite, it was shown by lattice analysis and X-ray diffraction that the nucleation and growth of the protein crystal on the mineral was likely to be truly epitaxial.

Mcpherson, Alexander↗

NASA NTRS1987

Facilitation of the growth of protein crystals by heterogeneous/epitaxial nucleation

A preliminary exploration has been made of the effect of inorganic crystals on the nucleation of protein crystals. Four representative proteins were crystallized by the vapor diffusion technique in the presence of fifty species of inorganic crystals. A substantial decrease in critical supersaturation was caused by thirty nucleants for canavalin and by seven to fifteen nucleants for the other proteins. Several cases of anomalous morphology were observed, as well as one instance of epitaxy, i.e., lysozyme on apophyllite. It has thus been shown that inorganic crystals can be used as heterogeneous nuclei or epitaxial substrates for facilitating reliable and controlled nucleation in automated protein crystal growth experiments.

Mcpherson, Alexander↗