Thrombin-thrombomodulin activation of protein C facilitates the activation of progelatinase A.

The activation of the matrix metalloproteinase progelatinase A (MMP-2) has been of keen interest because an increase in MMP-2 activity has been implicated in disease states such as cancer and atherosclerosis. Activation of MMP-2 occurs on the surface of specific cell types in two steps. In the first step, primary cleavage of MMP-2 by a membrane-type matrix metalloproteinase generates an intermediate.

Thiamine deficiency decreases steady-state transketolase and pyruvate dehydrogenase but not alpha-ketoglutarate dehydrogenase mRNA levels in three human cell types.

Reductions in the levels and activities of enzymes that utilize thiamine diphosphate (ThDP) as a cofactor are thought to be responsible for the tissue damage suffered during thiamine deficiency. Although loss of cofactor can account in part for loss of enzyme activity, thiamine and its phosphorylated derivatives may also regulate the expression of the genes encoding these proteins. To examine this possibility, steady-state mRNA levels for three ThDP-dependent enzymes were measured in human fibroblasts, lymphoblasts and neuroblastoma cells cultured under conditions of thiamine sufficiency and deficiency.

Thiamine pyrophosphate-requiring enzymes are altered during pyrithiamine-induced thiamine deficiency in cultured human lymphoblasts.

The most common of the severe complications of thiamine deficiency are beriberi and Wernicke-Korsakoff syndrome. To help clarify the biochemical basis for these disorders, a cell culture system has been established in which pyrithiamine, a potent thiamine transport inhibitor, was used to mimic different degrees of thiamine deficiency within human lymphoblasts. Activities of both transketolase and alpha-ketoglutarate dehydrogenase (alpha-KGDH) decreased at the same rate and to roughly the same levels in response to thiamine deficiency within a given cell line.

The thiamine-dependent hysteretic behavior of human transketolase: implications for thiamine deficiency.

We have investigated the hysteretic properties of human transketolase with emphasis on its dependency on thiamine pyrophosphate concentration. As demonstrated previously, the reaction progress curves revealed a slow transition from an initial low velocity to a faster final steady-state velocity, characterized by the rate constant tau-1. The rate of the transition was dependent on the concentration of the thiamine pyrophosphate cofactor, with progressively longer transition times found as the concentration of thiamine pyrophosphate was decreased.

Thiamine utilization in the pathogenesis of alcohol-induced brain damage.

There is increasing evidence for the role of thiamine deficiency in ethanol neurotoxicity and in development of alcoholic organic brain disorders other than Wernicke-Korsakoff syndrome [WKS] and cerebellar degeneration. Investigations in humans and in animal models have implicated a reduction in the activities of thiamine-utilizing enzymes as the metabolic basis of tissue injury due to thiamine deficiency. We have investigated the interactions of the thiamine-utilizing enzyme transketolase [Tk], derived from human fibroblasts, lymphoblasts, and various brain regions, with its cofactor, thiamine pyrophosphate [TPP], in an attempt to elucidate the molecular basis of selective brain damage in alcoholism-associated thiamine deficiency.