Estimating lysozyme crystallization growth rates and solubility from isothermal microcalorimetry.

A microcalorimetric technique has been developed to measure crystal-growth kinetics and enthalpies of crystallization. The enthalpy of crystallization of hen egg-white lysozyme in 0.1 M acetate buffer at pH 4.6 was determined at 287 K using this technique. The enthalpies were directly measured to be -14.3 +/- 2.0 and -14.6 +/- 1.3 kcal mol-1 (1 kcal mol-1 = 4.184 kJ mol-1) for 3 and 5% NaCl solutions, respectively, which is in good agreement with values estimated from previous solubility measurements. Non-linear regression of the transient heat flow allowed measurement of the crystal growth rate as a function of protein supersaturation as well as the solubility. The crystal growth rates determined by this method were found to agree with those in the literature under the same solution conditions.

Medical students' perceptions of desirable characteristics of primary care teaching sites.

PURPOSE: With the increased need to establish primary care sites, we must identify the key characteristics of effective primary care training experiences. METHODS: After completing a required year-long primary care experience, third-year medical students participated in focus groups (n = 17) and completed a Q-sort exercise with three sets of items: preceptor characteristics, site characteristics, and a combination of preceptor and site characteristics (n = 59). RESULTS: Thirty-eight concepts were identified by content analysis, which were grouped into six major categories: patients, preceptors' teaching behaviors, characteristics of office and staff, preceptors' personal characteristics, programmatic issues, and educational opportunities. The focus groups clearly identified preceptor teaching characteristics (35%) as the major factor that determines a good primary care teaching site. Items with the highest rankings from the Q-sort exercises related to teaching characteristics of the preceptor. The preceptor's enthusiasm, genuine interest in students, and ability to involve the student in active learning experiences with increasing levels of student responsibility were rated high. CONCLUSIONS: The development of primary care experiences should focus on the selection and/or development of preceptors with the identified personal and teaching characteristics. Preceptor rather than site characteristics seem to make the vital difference in primary care educational experiences.