Biomedical subjects

Jin Yoshimura

Publications and source records attributed to Jin Yoshimura.

3 recordsLinked to original sources

PubMed2006

Stage-dependent density effect in the cell cycle of budding yeast.

Yeasts in culture media grow exponentially in early period but eventually stop growing. The saturation of population growth is due to "density effect". The budding yeast, Saccharomyces cerevisiae, is known to exhibit a stage-dependent cell division. Daughter cell, which gives no birth, has longer generation time than mother, because daughter needs maturity time. So far, investigations have been restricted in exponential or non-crowding state; very little is known for the stage dependence of density effect. Here we present a lattice gas model to explore the population dynamics of crowding period. We compare theoretical results with experimental data, and find a stage-dependent density effect. Although small daughter cells can develop to a critical size, the reproduction of large daughter cells suddenly stops when the total density exceeds some critical level. Our results imply the existence of an inhibitor that specifically halts the reproduction of matured daughter cell.

Cell Count↗

PubMed2006

An effective method to increase solvability in biochemical systems using S-system.

In this paper we propose an effective method to estimate the intrinsic values in an immobilized enzyme system, i.e., Michaelis constant K(m) and the maximum reaction rate V(m). We combine three techniques: (1) the non-linear least square method for estimating the kinetic values, (2) orthogonal collocation with the Gauss integration method, and (3) Newton-Raphson method (NRM) or S-system method (SSM) as Newton-like method. We build a procedure to combine the first two methods to estimate the unknown kinetic values in a system. We apply this procedure to solve the intrinsic kinetic parameters determination problem in an immobilized enzyme systems following Michaelis-Menten reaction. To demonstrate the effectiveness of the current method, we test their convergence performance in detail. The results show that the basin of attraction in the current method is extremely enlarged compared with that of the S-system alone. We suggest that the current method is one of the most effective ways to solve fairly complicated biochemical reaction systems in general.

Enzymes, Immobilized↗

PubMed2002

Temporal changes in testis weight during the past 50 years in Japan.

The ever-increasing presence of environmental toxicants and their disruptive effect on the reproductive systems of wildlife raises the question of possible damage to the human reproductive system. Using medicolegal data from over 20,000 Japanese men subjected to necropsy from 1948 to 1998, we investigated temporal changes in testis weight to find possible evidence of male reproductive disorders. We also carried out a histological examination of 747 testes collected from 1978 to 1998. Our detailed analyses of the development of testis weight over the past 50 years have revealed four clear phenomena: (i) the age at which testis weight reaches its maximum has decreased; (ii) peak weight showed a general increase until it started to decline in boys born after 1960; (iii) the decline-rate at which testis weight decreases after its peak has greatly accelerated; and (iv) the onset of increasing testis weight of boys has occurred at a progressively younger age. Our quantitative analyses of testis weight indicate the possibility of a subtle reproductive disorder in Japanese men, especially in those born after 1960. Together with the accelerated development and decline in testis weight during the past 50 years, the decline in peak weight might be indicative of a subtle interference of environmental toxicants with male reproductive organogenesis.

Adolescent↗