Mayorga O L, van Osdol W W, Lacomba J L, Freire E
Department of Biology, Johns Hopkins University, Baltimore, MD 21218.
Proc Natl Acad Sci U S A. 1988 Dec;85(24):9514-8. doi: 10.1073/pnas.85.24.9514.
A multifrequency calorimeter has been designed to measure the amplitude and time regime of the enthalpic fluctuations associated with structural or conformational transitions in biological macromolecular systems. The heat capacity function at constant pressure is directly proportional to the magnitude of the enthalpic fluctuations in a system. Biological macromolecules undergo thermally induced transitions of different kinds. Within the transition region, these systems exhibit relatively large enthalpy fluctuations that give rise to the characteristic peaks observed by conventional differential scanning calorimetry. The multifrequency calorimeter developed in this laboratory has been designed to measure the frequency spectrum of the enthalpy fluctuations, thus allowing us to estimate thermodynamic parameters as well as relaxation times. This information is obtained from the attenuation in the amplitude or phase-angle shift of the response of the system to a periodic temperature oscillation. This instrument has been used to study the gel-liquid crystalline transition of phosphatidylcholine bilayers. The frequency-temperature response surface for large dimyristoyl phosphatidylcholine vesicles has been measured in the frequency range 0.04-1 Hz. The data are consistent with two enthalpic relaxation processes with time constants on the order of 3.8 s and 80 ms at the midpoint of the main gel-liquid crystalline transition.
已设计出一种多频量热计，用于测量与生物大分子系统中的结构或构象转变相关的焓涨落的幅度和时间范围。恒压下的热容函数与系统中焓涨落的大小直接成正比。生物大分子会经历不同类型的热诱导转变。在转变区域内，这些系统表现出相对较大的焓涨落，从而产生传统差示扫描量热法所观察到的特征峰。本实验室开发的多频量热计旨在测量焓涨落的频谱，从而使我们能够估算热力学参数以及弛豫时间。该信息是通过系统对周期性温度振荡的响应的幅度衰减或相角偏移获得的。该仪器已用于研究磷脂酰胆碱双层的凝胶 - 液晶转变。已在0.04 - 1 Hz频率范围内测量了大的二肉豆蔻酰磷脂酰胆碱囊泡的频率 - 温度响应曲面。数据与在主要凝胶 - 液晶转变中点处具有约3.8 s和80 ms时间常数的两个焓弛豫过程一致。
